its a simple question
he wants to save on the AC, (maybe limited hookup) and have it auto switch to electric if the lp is empty
many fridges operate better on LP
especially in hot weather, where campground voltage is low because of all the air conditioner use
but the answer to the OP is No..
never seen that option
a DIY would require some kind of heat sensor wired to a relay, placed inbetween the 120v plug and the fridge cord
LP on hot stack. keeps relay open, so there was no 120v to fridge
when the lp ran out, the stack would cool and the relay would close and LATCH (would need manual reset after refilling LP)
allowing 120v to fridge
fridge auto circuit would select electric
PITA job
just select manual LP and don't run out