Mel , I’m assuming each section would be glued up , screwed, stapled , whatever (the wood bits) , Then the whole sub assembly would get the mix , then foam glued on ... (GG does stick to the mix ) ..
At this point I’d be wanting a Large size FLAT assembly table ... But I know, having no table that size , I’ll end up crawling around on the floor for this (knee pads indicated)
Considering half lap wood joins for the cross members, roof “rafters” , that would “key” into the side panels . Then foam applied over them , so we’d be thinking of a pre inside covered panels for the roof/ceiling , and perhaps staining the wood , since it will be exposed ..unless we wanted to fill in between the rafters , giving us a thicker , more insulated roof .. That’s always good eh ?
This is a lot more woodworking than I care to get into ... spoiled by the assembly of thick foam sheets ... Money I save on foam I spend on labor .. and at my labor prices , that gets EXPENSIVE quick ...

So it may be penny wise , and Foam foolish to worry about the price of the thicker foam ...
Ok, I ’m feeling much better about all this again ... I’ll just BUY (

) the foam I need and be done with it .... it’s still a Big savings whichever way I look at it ... Apparently , Thrifty also has to be Smart and Calculating..
Now she tells me : “ you know how claustrophobic I am ! “ ...

Great !!! Now she tells me ...
Stevexxx, I really like the idea of a Formica wainscoting on the inside , some of that modernistic stuff, half way up the wall ... maybe some cool wall covering up the rest and on the ceiling .. Decor !!!

This one will be to make the wife comfortable ... if possible
Ever since I mistakenly showed the wife that "I dream of Genie" interior , that’s what she’s expecting ...
