I dont think the switches will let you run electricity and propane at the
same time. Dont know, never thought of trying it.  The ammonia solution
needs to be a rather specific tempature. Ammonia needs heat to seperate
from it's companion chemicals. It is this pure ammonia vapor that absorbs
the heat as it then condenses at the top of the evaperator pipe.

This black pipe is where the aluminum ice cube tray holder is clipped.The
top of this dead end pipe is behind the ice cube tray area. This is the
coldest part of the pipe,and the highest ,physically for the ammonia vapor.
The vapor collects here in a cloud, and condenses.The ammonia "rain" runs
back down the pipe and into the rest of the soultion, that it had left,
when first heated.If there is any uncondensed ammonia, it will condense a
few inches further down the slope,were there is more heat to absorb.If your
system is working properly, frost should form all the way(and quickly)
across the black pipe that is inside the frig.Frost should form around the
90 degree bend and stop at the place where it enters the rear of the frig
box.Still, it is far colder at the top of the slope.Good place to make
ice,huh?Extra heat may only make,the sloution  overheat, and crystalize
somewhere in a small passage. Same, I am told if you operate the frig off
level and the van is not being driven.This is supposed to be rare,though.
Anyway, the added heat will not seperate out this ammonia solution any
better. It will add extra, unneeded heat load to the frig,and reduce it's
capicity.Also this extra heat will make you warmer than necessary. The
waste heat is only exited the van by the flue,and not all if it gets out.

Seems that a heat shield between the ammonia pipes and frig box is a good
idea. Kinds like muffler or exhaust pipe heat shield. Just a small break of
space to reduece the heat actually getting to the box. How bout a piece of
aluminum roof flashing?