Poly vs stainless tanks ?


Both have pros and cons.

Rotomoulded food grade would have been my ideal choice, if i didn't need a custom size.

I approached a few plastic tank makers with my scale template, but they were keen as they didn't haven enough width to get the plastic welder in.

So i made my own out of 8mm food grade HDPE, and plastic welded it, its quite an easy material to work with, as i'm a cabinetmaker and i already had the tools to cut it.

Although i had to scrap it, as the issue that the plastic welders pointed out previously was an issue, and i just couldn't sort out 2 pin leaks.

So the new one is 2 mm 316 SS with baffles and haven't had any issues yet, I used Sodium Percarbonate to clean it before fitting it, i do need to clean it again before we hit the road.


Well-known member
If you go with poly tanks, consider a "welded" in metal insert threaded to accept your drain plug. It's pretty easy to foul threads in plastic materials if one even slightly over tightens a bung. If you have the space you could also consider a low profile valve for your drain plug and avoid thread problems all together. We've found we use the drain plug more than expected:

1. Removing all water from external tanks in winter.

2. Accessing water in the tank when some plumbing/pumping problem develops.

To save wear and tear on the tank drain fitting I have a PVC bushing in the tank fitting installed with a wrench. The plug goes in hand tight.

Ideally the tank is made with fitting(s) that are 1 size larger to accommodate the bushing.


Well-known member
One of my thoughts of going with a SS tank on my X-venture trailer, was I could run low voltage heating cables around the tank, to keep it from freezing in lower temperature trips. I do know you need to be careful with baffles, as the tank that came on my X-Venture is 2 11gal plastic tanks with a rather large baffle between them. In essence I never get to use more than 11 gallons. Schutt has since changed to a much smaller baffle after much customer complaints. I need to do something as I never get to use all the water I bring along, and the propane water heater doesn't work more than 2 minutes in freezing temps.


Crazy Person
I would think that this would be dependent on the thickness of the tank and what sort of terrain you plan on going over.
My plastic tanks are 10mm thick and are pretty strong. I have a solid base frame, which includes a 3mm aluminum sheet. The aluminum protects the bottom of the tank from stones and also helps to negate sagging.


Well-known member
thanks for everyones help, do plastic tanks need to be supported in all planes with plywood?
It depends on the dimensions, wall thickness and mounting.

Best to fill the tank to determine what needs supporting.

A welded tank of the same thickness need more support than a roto moulded tank.

Most tanks in mass produced RVs are 1/8" roto. These are hung from lips along the top edge. The bottom of the tanks will drop 2"-3" when filled. I've read forum post in which crossbars have been installed afterwards to support these tanks.

The top of RV tanks will drop/sag/stretch over time causing a reduction in capacity.

I wanted the (approx 14"Hx34"Wx60"L) tanks (3/8" welded and 1/2" roto) in my trailer to be insulated. The tanks were jacked/pressed up into steel frames lined with 2" XPS (extruded poly styrene) foam. All the tanks sit on 2" XPS but the tanks over the axles (limited clearance) are held up with 1/4" (5052 grade) aluminum while the tanks ahead of the axles have 3/16" aluminium with stiffening bars (6061 grade) welded (5356 grade wire) on.

All tanks are sloped 1/4" per foot to a drain.

The drain (3/4") in the water tanks is in the bottom which allows 100% (tested) of the water to be drained out when we are not using the trailer.

The water going into the tanks is filterd to 1 micron

The tank guage is an I Series. The tanks have internal sensors because a Moda sensor will not work on a tank wall that is more than 1/4".



Hmm, tank sensors, a whole another topic, I went with Ultrasonic sensors linked to my Victron Colour Control via a NEMA2K network, not cheap but works a treat.

I couldn't find an internal one that didn't have bad reviews over time.

Cheers Steve


Active member
You guys are the best. That was going to my next question :). I was thinking the same thing Steve did with Victron. What sensors did you link to the Victron ?


Hi Cam, I used Maretron TLM-100 sensors. The Victron CCGX has a custom front screen for motorhomes that shows all the power stuff and up to 4 tank levels on the same front page, makes it real easy for the bride to see what she needs to.

I shouldn't need focus tubes as only interested in readings when parked up. Make sure to put the mounting holes far enough from the tank edge and fittings, or use a focus tube.

You also need a gadget to program the sensors, I bought a Maretron USB 100 2nd hand off a guy in the states for $100. There are other things that will do it as well and I think there is some program functionally via the CCGX but haven't confirmed, my local boat shop could also do it for a nominal fee. Maretron has all the software and drivers. I did a dummy setup in the lounge using a laptop and sensor in a bucket. Was impressed with how well they work.

For the N2K bits I bought a starter kit from a local boat shop and the rest online, Maretron have a builder program that you can use to generate a parts list. This is all marine gear so dear as poison so consider what bits you need wisely. For instance it was far cheaper to use a 4 port N2K hub and run drop cables from each sender than individual nodes. Have to buy Victron own's N2K interface thou.

I got the sensors and most bits online from the US, exchange rate was better then thou, still for 4 tanks was about $1100 oz all up, not cheap but great result.

My tanks will be fitted shortly so keen to see how they go.

Cheers Steve

Edit: There are other cheaper ultrasonic sensors but not N2K so the interface bits for the Victron worked out far more expensive. But look around as this tech is evolving.


gait, I have to make a few tanks, any suggestions on where I would learn about building tanks?
first bit was learning how to plastic weld. A little practice. The basic is the design of the welder, the rod that matched the welder and the job, temperature, pressure, and speed. A good weld looks consistent, with the mark of the heel of the welder on the rod, not completely melting the rod. There's a couple of websites I used 10 years ago - I'm on a slow internet link in bush at the moment. After a few welds a good one "feels right".

My welder cost about A$800. Leister. I have no idea what the eBay copies are like, they weren't an option when I bought. An aside, I've used it for lots of things, including fixing leaks in PE tanks with old mild containers, strengthening a cracking kayak, etc.

My tanks are rectangular. Largest is 150 litres, with one baffle. Others I used 6mm food grade PP and 6mm welding rod (actually triangular with rounded outer face). I added an extra thickness of PP where there would be in and outlets then drilled and tapped with 1/2" BSP (which isn't 1/2" at all). Then screw in plumbing fittings.

I got ambitious and added copper coils to keep tank warm from webasto diesel heater or engine in cold weather. I wanted the coil to be continuous inside the tank, no joins, so made some PP glands with standard screw on fittings with collets. Really a bit of overkill for where I've been (lowest -10 deg C).

The tank brackets are 50x3mm mild steel strip. "L" welded to sub-frame. Tank strap tightened against the bottom of the "L" to push against truck floor. A sheet of 3ply under the tank, tank strap rubber on the straps. No support on sides. I also had small "wings" on the sides to stop for and aft movement against the tank straps.

The first one I made had a couple of small pinhole leaks. Just had to be dry to reweld. After that my technique improved. I welded inside and out, then put the top on.

Interesting bit of design - it was easier to install them from above, with subframe in place on vehicle chassis, before fibreglass panel floor glued to subframe then body built. But they had to be removable from underneath, just in case. I had to remove one on the roadside when a tank strap broke, to get access to drill and bolt a bit of steel to repair strap. A one-off design and build is always interesting ......

So far so good. About 10 years and 34 countries on fairly rough tracks.

I have a flow meter with an Arduino to count pulses to show usage on a simple display.
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thanks for everyones help, do plastic tanks need to be supported in all planes with plywood?
Like Gait, none of our HDPE tanks are supported or protected in any way except for two 50mm wide x 3mm steel support straps each. That includes the two 70 litre x 3mm wall thickness commercial ones. In a couple of cases I have hot air welded extra bits on to a tank to protect plumbing from rock damage.
14 years, 200,000km+ and no failures or damage.
OKA196 motorhome


I originally had brass threaded inserts moulded into my HDPE rotomoulded tanks, but found that if they were over tightened, even slightly, that they would then leak. A different style of insert may have performed better. I subsequently cut many of them out and replaced them with spin welded plastic ones. They are a bit soft, so care is still required, but replacement is not a big job.
Spin welded ones also simplify the mould design as they are a post mould operation and each tank can easily have fittings in a different place.
OKA196 motorhome

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