A gift from my father ...

[KCStudly]

Not to take the wind out of your sails, but I think it has been done. Wish I had a link for you. IIRC the guy had a very good experience with the particular contractor he used, and he had some useful advice on what to expect. Again, IIRC, he was in home construction and had some prior dealings with a couple of these vendors.

Maybe Norm (Mezmo) will pipe up (he's really good with remembering and being able to reference these things).

[Wolffarmer]

I do remember someone that did something like this. Built the TD with stringers much like and inside outside house. Had it foamed and then after trimming off the high spots put the outside sheeting on. But this type of construction has wood stringers in the walls so the foam is not a complete uninterpreted shell. Which I think is what you are aiming for.