Mark, as you have a wood box type storage and unless you are using the side compartments for other stuff, this would be a good spot to flush mount the plug(s). I used the same cheapy (2.99) Wal-Mart plug with the spring top (water resistant) under the hood for my Helton shower plug in. Also, used a cheapy one that looks similar to the one you already (with a plastic plug lid) have and cut a hole in the side compartment that is flush with the back doors on my 73. With the larger barn door (with spare tire on it) closed it will not let the plug bounce out. Also, easy access to unplug and see the green light to make sure all is well with the food inside the fridge. I wired it to 24V so my batteries (24V NATO compliant) get used continuously rather than just 12V on one. I found that this works quite well for me.
Surprisingly, why are these plugs (especially the quality ones - read non-Chinese) so hard to find and so expensive when you do find them? OZ has some of the koolest gear, now why don't we get gear like that with as large a market that we have?