We have a engel (
MT27F-U1 ) Fridge, Freezer that we use for a freezer. If you put it to max cold it will blow up coke can. The link to the Engel is just the first one that I found. They cost an arm and leg but you will not find a better brand or lower current draw. I have our in the 4 runner with a battery and a 100 watt solar cell mounted in the roof rack and it will run 24/7, with out running the truck.
That said we use a lot of can goods and dry pack foods. If it is a road trip you only need a week worth of food, there is always some place to buy food. Also if you do a cooler, ice is easy to get. We do bottle water for drinking and we will just fill the tanks with any water we come across. Depending where you camp and they do not have shower you can normally stop at a up scale CG e and buy a shower for $5. A truck stop will be higher.
We have done 45 days in our A frame and had a great trip.