There's no substitute for gas refrigeration while boondocking, but after the 3 way fridge bit the dust on our 40 year old trailerable houseboat (that I use as a as a camper) I experimented with keeping stuff cold.
Because a replacement 3 way fridge would take 6 months out of my traveling budget, the dead 3 way was replaced by a ridiculously cheap 120vac dorm fridge with no freezer compartment. Making 6 ice cubes takes up way too much space to be of any use. Using a group 31 battery and inverter, I can get about 48 hours out of the fridge without charging the battery.
But the fridge became 'eminent domain' for my wife's lettuce and I needed a place for my beer. A very small chest freezer was the result. Now this isn't installed on any Forest River product - YET, but you may find it interesting if you have room for a small chest freezer. It's shown here on the back of the houseboat but might eventually be seen on the aft fold down deck of my Wolf Pup?
The freezer can be set from zero to 40 below. I decided to put a 5 gallon jug of water in the bottom, freeze it into a brick at maximum low temp while the rig is in the back yard on shore power, then unplug it and use as the freezer as a cooler while on the road or water. This setup yielded an effective 'cooler' (needing no ice) for 6 days even with moderately heavy use.
But, wanting my beer to be colder than the melting ice would provide, I took to studying eutectics and found that by adding salt to my jug, I could lower the melting point - 24 oz of salt to 5 gallons of water would yield a melting point of about 28° --- and I've been a happy camper ever since.
The problem here is, that on a planned month round the US trip, we'll eventually need to recharge the 'brick' and the thermostat's highest setting is zero so my beer bottles/cans will burst from freezing. Ah, but I've got that covered in another post if y'all are interested.