The underbelly and compartments are heated, but I am not sure if they are cooled. I know they are lots cooler than the outdoor temp in the summer, but I honestly have no clue if they are cooled, or if it is a result of the cooler rig above them.
The compartment/underbelly heat is via the gas furnace, which can be an issue. The furnace uses lots of propane when it is set at 72* and it is freezing outside. We actually have a 100gal propane tank that DH used to supplement the on-board tanks.
The garage is heated and cooled, also. It seems that most of that heat rises up since the ceiling is so high, and leaves the floor cold. People have talked about putting reflectix and/or carpet padding under the garage carpet to help make the floor feel "warmer". You'll also need to run some of the electrical heaters off an external extension cord directly from the power pedestal outside. If you try to run them all off the outlets in the camper, you will blow a breaker. DH also lined EVERY window in reflectix, and put it behind the couch to keep the drafts down. We've left them up for the summer, too, only taking them out of windows that we want to see out of. It does seem to help keep things cooler...
There are other forums on here that have lots of fulltiming members. They are a wealth of info on "how-to's". It is a bit harder to find info on fulltiming with kids - there are families out there that do it, though. You might want to do a google search, as I know a few families have very informative blogs. They may help you decide if a bunkhouse or a toyhauler fits your situation better.
