My little version of warehouse 13.
I lined the inside with 1 1/2" foam insulation. It makes a huge difference. When it was cooler out and you went in there, you could feel the steel walls just radiating heat they soaked up from the sun like crazy.
The 1.5" of foam makes a huge difference. We've been having some unseasonably warm days, up to around 90, and I've been working out there and it's amazing how comfy it has kept the temperature.
I used liquid nails to put things in place, but in reality the way I cut it and put things together, the sides would actually hold the roof panels up, should the LN fail. But so far, everything is holding together.
I'm not all that worried about condensation, because, hey, it's the desert, and we are pretty darn dry here.