Why do you apply Luan on to filon?

....Crane Composites manufactures FRP (chopped stranded fiberglass panels) in many, many grades. The thinner and least expensive FRP rolls/sheets have higher moisture pass-through. Also, manufacturing hung or composite RV shells/walls requires exceptionally clean facilities (atmospherically controlled and dust controlled lamination room). You'll want to get a tour of any potential RV manufacturing facility's "lamination room" as part of your buyer decision-making due diligence. The Crane Composites fabrication engineering notes are very clear:

"CCI recommends that the moisture content of the substrate (lauan
plywood, or Azdel) be no greater than 12% at the time of lamination
and that the glue coverage between the Crane Composites panel and the substrate be 100% coverage at the weight and thickness recommended by the adhesive manufacturer. Prior to lamination the frp panel must be free of dust, moisture, particulates or backside contaminants to ensure 100% bond. The quality of the substrate
surface must also be free of dust or particulates prior to lamination.
CCI will not be responsible for any loss resulting from sub-standard
lamination processes."

So, if you do more research into what Crane calls "substrates", or the bonding surface the FRP will be adhered to, you may want to focus on the Azdel substrate, and its excellent moisture resistance. Also, the adhesives area is also very critical (depending on the adhesive chosen by the various RV manufacturers, there is another set of adhesive application criteria that will usually involve application using very tight (PLC) process control automation).

Concluding, manufacturing an RV (or, any other road-going unit) shell with FRP paneling is a very, very finicky manufacturing operation, requiring extremely tight process control...

Good luck in your hunt for an FRP-clad shell.

Jeepers92 wrote:
Why could you not glue the luan to the camper frame work, then glue the filon to the luan?

I couldn't do it because I don't have the capability to build RV walls. I doubt that anyone has the capabilities to build RVs in their garage, regardless of what steps are used.

The question should be, why use luan at all. Has to be the cheapest least water resistant material on the planet yet they use it in situations where it is pretty well guaranteed to get wet and fall to bit.

Just a guess, but I imagine getting all the bubbles out between the filon and luan while working on the side of a camper could be an issue. Much simpler when you can run the sheets between rollers to push out any air pockets.