We used to travel with our ferrets and cats in cages inside our 5er while driving with the dogs in the cab of the truck. We ran two Honda generators (parallel connection) so that we could run the air conditioner, my husband added eye bolts to the truck bed to strap them down securely. We even made a rain cover so that they would stay dry if it rained - it was also strapped down securely when moving (the cover was a box made from PVC pipe that I sewed a tarp to fit it) this cover was used on the ground at NASCAR races when we were boondocking, too. I bought an outdoor digital thermometer to use, zip-tying the sensor unit to one of the cages, and had the monitor in the truck so that I could know what the temp was in the 5er. (The cages were in the front nose wardrobe closet located above the hitch so they have a very smooth ride.)
The ferrets and cats went all over the country from Yellowstone to Maine to Florida. What great memories we made and everyone stayed together. We never had a problem running the air conditioner while traveling over many many miles.