RE: What to do with the 110 V AC oulet under the sink when installing 12 V
DC fridge

Neil, here's what I did and it's worked perfect for me.  When I installed
the Norcold I had to do something with that wall out let also.  I went to
Lowes and picked up a nice beefy single outlet meant to be pu on the end of
stock Romex wiring like the line coming to that two outlet box.
Disconnected the orignal box and discarded and put the single oulet on the
line.  Then (here's the good part) I connected/plugged in a six outlet
power strip, ran the cord through the gap at the back of the cabinet and
then mounted the power strip on the end of the sink cabinet, at the top,
right behind the drivers seat.  Now ALL 110 connections are made to that
strip.  My inverter is mounted just below and the 12v oulets mounted below
the inverter.  So any and every item that needs to be plugged in has it's
wires right there, in that corner, behind the drivers seat.  No wires/power
cords running across the floor, everything out of the way and not stepped
on or tripped over.  And I use an electric cube heater also.  I place it
right on the floor in that corner, right in front of the big cabinet door.
Out of the way, pumps its heat back toward the bed area, and no getting in
the way.
I actually mounted the 110 power strip many years ago and that has worked
great.  And no having to figure out where to cut holes and mount things
with hot 110 V on the back of them.