My Catalina has a 6 cu ft ice chest. We bought it when it was 10 years old and it came with a 2-compressor Norcold system that pulled 10 amps and ran half the time. That works out to 5 amps average or 120 amp-hours /day! A friend had the same boat, same setup that was the same age. We looked at Adler-Barbour but being gearheads decided to make DIY systems. The compressor was the same Danfoss that AB uses. The evaporator (coil) was custom made from 3/8" tubing to fit the shape of the freezer box and used an expansion valve instead of the capillary tube. Capillary tubes work fine (every household refrigerator has one) but they must be matched to the size of the compressor and evaporator. As our were custom it was easier to go with the expansion valve. We also upgraded the so-so factory insulation with additional spray foam on the outside where we could reach it and added 1" of fiberglass-faced blue board to the inside of the deep freeze compartment.

We now have the 1 cu ft freezer that stays at 0°F and the other 5 cu ft of refrigerator at 36-40°F. The daily draw during Pacific Northwest summer days is about 25-30 Amp-hours with normal cruising mode use. If idle at the dock it is less than 20 amp-hours / day. I think the reason for the low draw is the Danfoss compressor is way more efficient than the old Norcold and also the improved insulation helps. (see Dave's comments below). I would love to have the 8" of insulation like Gene has but that would require a total remodel.