It is insulated. I believe its just fiberglass insulation between the exterior aluminum and interior wood paneling.
I had mine set up pretty standard; only a couple inches taller and a couple inches longer on the cabover. The roof rack was extra too. I also had them install a fantastic fan instead of just a vent. The windows are standard in the rear doors but it can be built to your specs with or without. Ive even seen them with one door, hinges, the one they built before mine was designed to fit with the tailgate on (like a fold down patio for the double doors) I believe it was for a Tundra.