RV Repair: RV Roof Replacement, rigid foam insulation, wood trusses

Question
I have a 1978 RV and I need to replace the entire roof system.  It look like all that is there currently is a 3/4 inch rigid foam insulation layer sandwiched between two layers of paneling.  I have tried to replicate this system but have been unable to get anything rigid enough to span the RV.  I have also tried using wood trusses but am also having problems getting anything rigid enough with only 3/4 inch of height.

Thoughts?

Answer
Mark,

      I would try wood trusses that are made from 2X4's.  Leave about 20" in the center at full 4" height and then from there to the edge cut them at an angle down to your desired height at the sidewall.  You may have to go a little more than 3/4".  Then I would cover the roof with a minimum of 3/8" plywood and glue a new rubber roof down.  Before you put the trusses in place I would lay the new ceiling panels in place and then attach them after the trusses are mounted.  Don't forget the insulation before you put the plywood decking down.  I hopethis helps and good luck.

Darren