Thanks to Dennis and other listmembers who got my on the right track
to fix my fridge's 12V operation.

First, I was surprised to discover that the fridge gas LED also
glowed under 12V operation. Finding out that was normal took one red
herring out of the hunt.

The action I THINK I took to fix the problem was to tighten the screw
holding the relay to the metal under the driver's seat. Whether it
was this itself (I don't know if that relay grounds through the metal
case, or if just messing with connections made the difference), a
thermometer placed on the ice cube plate came down from 70 to 40
degrees after about 15 minutes of idling and then 15 minutes of
driving. I am going to try to simulate "normal" operations (running
the fridge overnight on LP or 110 to get it cold, and then see if the
12V operation keeps the thing passably cool) before I call it quits,
though.

Jim