I have an Adler Barbour that is a spill over system (it's a freezer really) with a pretty large freezer and frig. I keep the freezer about 20 degrees F and the frig about 35 degrees and on average it uses 60AH/day based on solar panel log during the week.
We use a Domatic cooler/freezer. It is 12/24Volts DC or 110Volts AC. We run it on DC on the boat as a cooler with the temperature set at 1 degree C (Appx 34 degres F).
LOVE IT! Uses very little power and is almost silent.
At home in our northern winters we set it to -17 degrees C ( Appx. 2 degres F) and use it as a second deepfreeze on 110Volts AC. Have had it two years with no problems.
We have one of these, for day use it might work. Does exactly as is says, holds at 40 degrees, or a bit more, less than the outside air. Draws about 5 amps, IIRC. Pre chill with the 110 volt converter at home, plug it in to the car while driving to the boat and you are good to go.