Underbody storage solutions


I’ve got quite a bit of empty space under my van, including at the rear between my leaf shackles where the spare tire used to sit.
I keep thinking it’d be a great spot to make some kind of slide out storage deal to carry heavy/dirty tools etc that I’d want to keep outside and down low to help the COG.
I’d also like to use it to mount a water tank but I could do that in other spots. Or vise versa.

Just looking for some pics or write ups for inspiration, anyone got anything?


New member
I've seen a bunch of people put a secondary fuel tank where the spare was. I'm sure a water tank would work just as well. I want to move the spare out from under my suburban to expand on my fuel capacity (9 MPG doesn't get me as far as I'd like between fillups) I've seen people make/mount custom fuel cells and ive seen people just find tanks in the junkyard that fit good enough for their purpose.


To me the big issue with an additional fuel storage area/tank is transfer of fuel. there are many ways to accomplish this without interconnection of the tanks as many of the later fuel systems are 'sealed'. One can incorporate a switched remote pump control to facilitate transfer.
I removed my spare to a rear swing out bumper mount and located two Nato petrol cans into that space. But many would not want to handle the weight of the cans with fuel in them although it does keep the COG lower than mounting on the roof rack as many do.
The idea of a custom fuel cell has a lot of merit.

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Expedition Leader
not so much 'sealed' as air-tight for emission control reasons, usually a controlled purge cycle where a vent solenoid is opened and an evap cannister's contents are drawn into the intake / combustion cycle. If your extra tank isn't airtight, you'll get some emission error codes thrown. Simple enough to incorporate a valve in the fuel transfer plumbing so the factory system remains 'sealed' during normal operation.

being in the desert southwest I second the idea of a nice capacious potable water tank in the undercarriage. With the added benefit of all that fluid weight helping to keep center of gravity lower.


Active member
I was looking to add some extra water storage so I tried fitting a 15 gal water bladder in the spare tire location.
I used a plastic mortar mixing tub to contain it and strapped it to the frame with ratchet straps.
Where there was no easy way to anchor to the frame, I used Unistrut channels secured to the bed supports with Riv-Nuts. I think the full tank is about 130 pounds, behind the back axle but about the level of the cab floor.
Matching the opening on the tub is a plywood top (also attached to the frame) to keep the bag from moving around or out of the tub. The rectangular shape of the tub left me enough room to mount a 2.5 gal. air tank under the bed as well.
The whole arrangement is about 8" tall, so it is well protected and still flexible enough to endure scrapes and dings.
There is a hole in the plywood lid to access the fill tube and a hole in the bottom of the tub for the drain tube, which I can use to pump the reserve into my main water tank or empty into a bucket.
Filling is not too difficult- I attach a small hose to the drain and then secure it just above the hight of the top of the bag. With a hose on the fill tube, the bag will fill to the hight of the overflow without bulging too much.
With the fill tube opened as a vent, the bag drains at a reasonable pace and most of the water stored can be emptied out and used without lowering the tub.
The whole setup did over 3000 miles in a 3.5 week tour of southern Utah- rocks, washboards, deep sand and gravel roads without issue or damage. When I dropped the tub, there was a fair amount of silt, I imagine a good deal of dust found its way in and a few river crossings turned that to mud. The bag seemed unaffected and is still watertight.
The extra water let us stay out longer, take showers and be a little more relaxed with our water use.
The bag was fairly expensive, Aquatank2 it is called, $95 for the 15 gallon size online. The first one I ordered had a small seep around the fill tube, but the vendor sent me a new one right away and it has held up fine.
The other materials were on-hand or inexpensive, but getting the Unistrut fit in a plane and attached was a bit of work and making sure the fill and drain tubes stayed accessible while being protected also took time.