Azdel vs Vacuem bonded fiberglass

Terryallan wrote:
Azdel has no wood behind it as Luan does.

Correct, but a more accurate way of stating it is that Azdel uses a non-organic backing/substrate material.

Many/most(?) vacuum bonded fiberglass sides use luan plywood as their backing/substrate material. Luan plywood rots quickly is exposed to moisture. In a perfect world, no water would get in.

Filon is another brand name fiberglass panel made by Crane Composite, but there are several version. Some have wood substrate, some do not.

Azdel/Filon still can come "unglued" from the stud (typically metal) walls if sufficient moisture is allowed in. The fix is to expose as much of the back side as possible, use 3M "77" or "90" spray adhesive to re-affix the panel. Pressure is required until the adhesive cures.

Azdel has no wood behind it as Luan does. So rotting is not a problem. It is also supposed to be 50% lighter, 50% stronger, and have a higher R insulation value. You will have to check to see if the RV in question has it in the front, and back ends. Some do Some don't.
I do know my 30" TT, bunkhouse, with a slide weighs only 4811lb dry because of the Azdel. It is 7 years old, and is holding up very well.

Not sure I understand your question as a trailer can have both a fiberglass exterior with Azdel sheeting behind it, as did my own Coachmen Freedom Express. Where the issue blurs is when you read the word Azdel and assume it means all walls, which is usually not the case at all. My own FE had Azdel sidewalls but the rear and front walls were conventional wood behind the fiberglass exterior.