I ended up puting 1.25" of foilbacked foam into the roof before covering it with roll wave PVC roofing... it was flexible enough to roll down across the 45 dergee edges of the roof to the wall... and it is easily removable to add wiring for lighting and or speakers...
and the walls got 3/4" (they are already 5/8" ply FRP) then they were covered with FRP panel also screwed into place so future wiring and or plumbing will be simple...
Finally gave up on an intermitant alt.... replaced with a remanned unit for $78... no core so i figure I will have the OEM rebuilt for a spare