What do you use for sheathing under Filon ?


New member
I am researching building my own travel trailer. It will be used "off grid"/boondock (dirt roads) so a good strong frame is a must. I will probably use Timbren Axle-less suspension for better clearance.

I want this trailer to last a long time so I am going premium with all materials. The floor will be 3/4" campsite honeycomb and fiberglass (guaranteed to never rot). Wall studs and roof trusses will be aluminum. Many travel trailer manufacturers are using a non-organic (no wood fiber) sheathing called Azdel. I can not find a source for it.

What do most DIYer here use ?

If you are using plywood, what "grade" and thickness and do you apply epoxy or epoxy and fiberglass for weather protection and strength ?


Active member
I build my walls using the sandwiched method. The core is highly skeletonized CDX plywood. On the inside, it's sheathed with 1/8" Baltic birch and 1/4" underlayment plywood on the exterior. The voids are filled with foam board. The construction aids in strong joinery.

And yes, fiberglass/epoxy on the exterior walls, roof, and hatch.

You can see my detailed build log over here: http://www.tnttt.com/viewtopic.php?f=50&t=71588



I you want a ply exterior, I wouldnt use anything short of a legit bs1088 okoume marine rated ply.
I have trouble trusting even baltic birch these days. I'm finding delam issues, and voids, that the ply never used to have.
Quality seem to have dropped considerably.

4mm or 6mm marine ply, depending upon your specific application/needs.

Our entire camper is wrapped in 6mm marine ply.
Opoxy coated, joints glasses, and painted.

Been on the road since 2012/13, not once being stored inside or under a cover.


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Active member
If you want true premium click below. Dont use wood, use this glued to foam, look at the sawtooth unlimited thread for ideas how to build it. You could do normalish framing job using skeletontized plywood, fill the voids with foam and use this as a skin. If want you can get the aluminum skin in the thicker premium version.