Have you looked at NovaKool or TruckFridge models? Either are made to be more durable than a cheapie "dorm fridge" fresh off the Chinese boat, and likely use less amperage.
I like the idea of building from scratch, but I don't have the tools, so I'm probably going to see about the Erwin Hymer budget model on the ProMaster chassis that Camping World sells, which uses an alternator to charge up a 200 ampere-hour lithium battery which is then used with an inverter to keep the A/C and other appliances going. The fridge on that is pretty puny, so I'm probably am going to add a TruckFridge chest fridge for additional capacity and tuck it near the passenger seat.