On the roof, we decided on one MaxxAir fan towards the front, and the rooftop AC with heating element towards the rear. The Maxxair fans are extremely nice because they can remain open in the rain. They also can take air in or blow air out, and have 10 speeds, ranging from extremely low power and silent, up to 800CFM. We placed the fan towards the front so it sits between the kitchen and bathroom, and can act as an exhaust fan for both.
For the rooftop AC, I chose the smallest unit I could find. The Coleman Mach-8 Cub pushes around 9000 BTU of cooling at about 1250 watts of power, or 6000 BTU of heating at 1750 watts. We can run this unit off a standard 15 amp household outlet, or a small generator. In theory, a few batteries and 2000w inverter would also power this unit, but I do not know if I'll be buying an extra battery simply to run the AC. I plan to add an additional furnace for regular use, but for the minimal cost of adding the heating element, I felt it was an easy choice to add it for times we are plugged into shore power.
While the MaxxAir fan works exactly as we had hoped, the rooftop AC unit is quite a bit louder than I'd like, and the heating element seems to not be working. We will sort the heating element I'm sure, but it's difficult to test in the heat of summer. The noise is simply the larger blower fan right above our heads. The unit actually seems quieter outside than inside. Luckily the noise stays consistent, rather than older AC units which would abruptly turn on and off to control temperature.
Finally, insulation! Their are endless debates about the best options, but I used my own past experiences to know exactly what I wanted to use. Mineral Wool insulation is moisture, mold, and mildew resistant, as well as fire resistant to over 2000 degrees. It's also readily available, reasonably affordable, and a little more efficient than regular fiberglass insulation. It's not particularly healthy, but all of ours will be encapsulated so I went with it. I filled as many cavities and spaces as I possibly could with the mineral wool, then I went through with expanding foam insulation to fill all the smaller cavities. I use the "window and door" type so it can't expand too much and flex the metal. After that, I wrapped the entire sides with an automotive "Sound Deadener and Heat Barrier Mat". This 1/4" thick foil faced foam provides extra insulation, a solid moisture barrier, and a cushion so I can screw my paneling to the metal of the van, and not worry about any squeaking.
I insulated the ceiling with 1" thick rigid foam board, again sealed with a layer of the "Sound Deadener and Heat Barrier Mat". The flooring was a little more challenging. I wanted the absolute miminum thickness, while still being an effective insulator. I ended up cutting strips of the 1/4" insulating mat to fill the gaps between the 'ribs' in the flooring, then laying a piece of 1/2" rigid foam board over it. The flooring we used also has a cork backing, which has a little additional insulating value.
Roughly speaking, our floor is insulated to around R-6, our ceiling is around R-9, and our walls are around R-12.