FRP Ceiling Installation Methods

Looking for some advice on FRP installation on the ceiling.  My original plan was to insulate with rigid, sheet in 1/4 ply and then install using FRP rivets.
 
My concern has come while working on the van over the last few weeks and seeing the large amount of water that drips from the ceiling with it being cold out.  When I go into the van there is actually ice on the ceiling like the windshield of your car.  The plywood molding and rotting over time is my main issue.
 
So the question is are others installing FRP ceilings directly to the studs and are they happy with that method or recommend something else?  My current plan would be rigid insulation and then direct mounting to the roof studs. 

daddywoofdawg


I would paint the foam side of the ply,just like you should paint the back side of wood siding before installing,It will slow or stop the wood from rotting.

Just a thought; Could you use Pressure Treated Plywood as a backer to eliminate any concerns of rotting or trapped moisture - problems? Its about $32/sheet for 1/2" at Lowes/Depot.
Also, you can find those screw buttons pretty easily at a RV supply store. Their like.15 ea.

What about your walls are they up yet? And if not spend some money and spray foam the hole truck. And then install 1/4 inch underlayment then you can glue your FRP board to it and hide all your screws. We used fast drying FRP glue.