Eagle , even the airplane Foamie guys prefer the GG ... over epoxy ...

No reason it wouldn’t work better canvas to canvas , or canvas to foam ... The trick (I’ve found) with GG is
not to put on too much !!! and just mist it with water if you must , NOT Wet it down ... It will cure (slower) with the natural humidity in the air , and I suspect the foaming actually weakens the glue a bit ... bubbles eh ?

Pre assembled panels would be the way to go cause’ you could do a “mock up” just to check the fits as you go ...
Spars , not unless you’re going to stand on it huh ...

The cabinets, shelves, walls, arch , all supporting the inner structure... the sock , the outer bits ...