You said "So you had luan sandwich walls with 1x2s? Sounds you have an awesome build. I would like to make mine possibly double 3/4" with the outer wall solid foam3/4" foam sheets paired with the inner 1x2s filled with 3/4" foam cut to fit within the 1x2 openings... is that exactly what you did?"
Yes I would air nail and wood glue outer frame and add some cross supports to add strength for standing on it and fill the spaces with cut to fit foam. I did all the walls that way and could stand on the roof at 180 pounds. I would secure the walls together with wood glue and long drywall screws. As you complete the structure it adds strength to the overall enclosure. The sheer strength of the glued surfaces on both sides of the wall returns high tensile sheer strengths much higher than even solid 1"plywood at a tiny fraction of the weight.
The just mainly foamie route gives an easy build for people not inclined to be journeyman Carpenters. I studied the heck on this forum all I could find about the torsion box/sandwich build and then just started building. 3 builds total and kept morphing away from over building that I started with. I still haven't done a foam only build but will some day with a plastic exoskeleton over it but who knows when as life flow determines a lot of things these days. There are a lot of people here who've done a lot of different things and be wise to read between the lines of what they would do after the fact.
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