Still in design stage

I have so many questions about this 'foamy' construction. Attached is a pic of my next trailer (still in design stage). I need to get the weight down and this system is intriguing to say the least!
First and foremost to me is how structural is the roof? Will it require 'stays' or just foam? I assume 1 1/2" thick.. I'm about 11'-9" long x 7'-5" wide.
[img]
[/img]
First and foremost to me is how structural is the roof? Will it require 'stays' or just foam? I assume 1 1/2" thick.. I'm about 11'-9" long x 7'-5" wide.
[img]