Here is what we did, right or wrong, it worked for us.
I used two inches of foam board and spray foam to beef up the insulation in our icebox. The first year out, I took apart a dorm sized refrigerator without breaking the system. I curled the condenser into a "U" shape. The evaporator went down into the box and the condenser and compressor went behind and on top of the icebox. I boxed the compressor/condenser in, with 3" holes at each end of the box. I installed 12 volt fans, like the ones used to cool desktop computers, inside the box at the holes. I purchased a Johnson controls refrigeration thermostat to run compressor and fans. I wired it up to my inverter
. It worked fine, but pulled more amps than my 85 watt solar panel and Aqua Air wind generator could put back in our batteries. The Honda generator had to be run way to much, about an hour each night.
The next year I got my hands on a used Danfoss BD35 12v compressor. I removed the 134 from the system, cut out the 120v compressor and soldered in the Danfoss, and put the gas back in. The Honda gets run much less now. We used it as a refrigerator but it would work as a freezer also by turning down the thermostat.
We sailed on a tight budget, and nothing on the boat had a factory warranty, but we sailed.