What you're proposing could be done but is probably the most complex way of doing it.
If it only runs on shore power then it's 120v AC, not 12v DC which is what you get from "upfitter switches". You would have to have an inverter somewhere to make the 120v AC. If you're going to install an inverter you might as well be able to use it for other things in the RV, like maybe watching TV with no hookups.
The simplest place to connect the inverter is the RV battery bank, not a switch in the cab of the tow vehicle. That would result in a long wire run that would have to be fairly large wire to handle the current and distance. It would also require and additional electrical connector between the truck and trailer.
Just put an inverter in the trailer, connect to the house battery(s), and wire it to the refrigerator outlet plus maybe a TV outlet or something.
