<p>Sika Sikaflex-221 Non-Sag Polyurethane Sealant Aluminum Gray is a one component, moisture-curing polyurethane adhesive sealant that is used for creating a permanent elastic seal for substrates such as metals, wood, paint coatings, ceramics, and plastics. It is a non-corrosive, low odor, high...
That's what Newmar uses to attach walls and ceiling panels to aluminum studs.
I used high strength contact adhesive to secure filon to ply and ply to foam (double check if the foam will be melted by your choice of adhesive!). Wet coat on both panels with flash time. Make a jig to exactly place your materials as you get one shot at getting the parts together. Use Dowels inbetween panels to help control your positioning. Roll out from one corner to the far corner to get rid of trapped air inbetween the panels.
Use headliner high temp spray adhesive to secure fabric to the ply (interior ceiling).