Thank you for this information. I'm looking at a 21 ft Sunrader remodel project where the entire rear interior has been removed, walls are completely stripped down to fiberglass and floor down to wood. Not sure if ceiling SIPS are intact or not, there was some water damage at rear roof vent, but still looks like there might be wood present, so perhaps panels have not been removed.
In looking at rebuilding in the rear do you have any thoughts on installing a lightweight but strong interior frame? Would it be worth the extra weight for the support? Not looking to overbuild/overload the vehicle as I'm aware of them already being heavy.
If ceiling panels have been removed would putting SIPS back in be the best way to go, or is there a better way if starting from scratch?
Have looked at some insulation options for walls (blue board panels, reflective air filled panels, spray foam), any feedback/thoughts?