First off, insulate, insulate, insulate. Then seal any joints/areas that might let in hot air.
I have used the CU 200 cold machine in several
boats using standard rectangular evaporators. They have proven basic, very reliable, relatively inexpensive, and easy to
DIY. My last two installations included a water-cooled option which has proved to be an excellent add-on as I spend all my time in hot, southern areas. The condensers have been in a
cockpit locker, to keep the
compressor heat out of the
cabin, but benefit from the
water cooling when the inside of the locker gets hot.
Keel coolers are OK but need frequent
cleaning of the outside of the tubes. I also saw a cooler mounted in a
galley sink drain hose, again a
cleaning issue.
Keep it sealed, keep it insulated, and keep it simple.