Using Upfitter switches to power my extra frig on the road?

If you want to run it while you are traveling, you probably shouldn't power it off the RV battery unless you have a big solar bank. So the solutions described above don't seem feasible.

Check amps on the fridge. Whatever it says, your wiring will need to handle 10X that much for 12 V power. Plus you will have some conversion loss through the inverter. So be sure your upfitter circuits can handle that much current.