Hi Russell,
I was involved in refrigeration and air-conditioning service, personally I like the 3 way in caravan/motor home set up as they are very simple, I realise you have had some issues with yours but this is probably more unusual than usual, have a think about how 3 way fridges work and they are silent, all you need for it to work is a heat source, 150 lt fridges normally run about 175 watt element, thermostat controlled on 240 direct on 12 volt, no moving parts other than the controls, attached how they work
http://en.wikipedia.org/wiki/Absorption_refrigerator
Compressor fridges only run on 12/24/or 240 volt transformer, and has a reciprocating compressor, (moving internal parts and noise) if you don't have enough power it wont run!
specs for the Waeco attached
http://www.waeco.com.au/products5.asp?id=508&catId=57&subCatId=61&subCatId2=72
Waeco have a BD50 Danfoss compressor, which is really the only compressor to have, stay away from fridges that run a 240 volt compressor with built in inverter, they aren't designed for mobile use, the springing in the compressor mounts are weak and will fail in time requiring compressor replacement
If you can keep the power up compressor fridges they will maintain set temp in all climatic conditions, but remember manufacturers quote power usage usually at 32 ambient, if the temp is above this it will draw a lot more current than quoted,
I hope this helps you decide what to do to find a solution to your problems
Cheers Greg