12t1, I'm using the RMAX
Thermasheath-3 insulation as it has the highest R-Value per inch of any insulation. The polyisocyanurate foam is a newer version/form of polyurethane foam.
Additionally the foil facing provides a 'Radient Barrier', do another search on this term as well. The radient barrier will reflect heat back into the conditioned space as well as reflect solar gain away (keep out) of the trailer during the summer months. With the method of installation that I have employed (foil taping the joints) I also pick up a 'Air Barrier' as well.
The 1/4" plywood has two functions, 1.) it provides the Thermal Brake from the conductive materials (metal framing) and 2.) provides a substrate for the final layer of rigid insualtion and finish interior paneling. The "Lite-ply" plywood I'm using has no VOC's in the adhesive, fyi.
This 'assembly' I believe will provide a robust energy envelope against extreme temperatures variations and provide for a comfortable environment within the trailer with minimal energy inputs (heating or cooling).