Hey, and welcome!
We have had a PuP, a Trailmanor, each of which had a 3.5 cuft fridge and our FF214WSD with its much larger fridge and have never traveled with the fridge operating. The PuP and TM both had the 12 volt option and we never used it and as gmw notes, the propane is the only option with the FF. We have nfever had any issues with the contents warming significantly; meaning the stuff in the freezer stayed frozen, even a small ice cream has remained cold enough not to be a 'milkshake' and we are often on the road for at least 6-8 hours before firing the fridge back up.
Now we live in the Northwest (N.Idaho) and we are 'allergic' to hot climates
, so we are not generally in 100+ degree heat. That said, we have traveled in the Pup and TM in 90s with same results. Part of trick is not to have the fridge nearly empty. Be sure it is at least 1/2+ full, pre-cool it for a day or two, and put already frozen items in the freezer before launch. Oh, and we don't fill the icecube trays during travel, just in case! But we've goofedon that before and not had a mess!
Hope that helps!