Azdel is the composite panel that Forrest River uses on at least all their Class C Motor homes of not more. It is the complete panel from the fiberglass outside to the foam interior to the inside panel and integrates into the metal framing.
Azdel is an exterior wall product. "Coachmen RV uses Azdel Composite Panels to replace wood in the RV sidewalls. Azdel Panels are constructed using a blend of polypropylene and fiberglass, creating an extremely strong and lightweight wall."
Could also try a clay bar (for detailing cars) if you don't want to use a solvent. I found it worked well for paint overspray, bug guts, and even stray sealant the factory had been sloppy with. I actually clay bar'd the whole motorhome recently prior to waxing. I use a little water spray to make dragging the clay easier.
2017 Forester 2291S
2015 Honda Accord on Master Tow Dolly
1999 Jeep Cherokee flat tow