While traveling the best ways to keep food cold is
- have your refrigerator/freezer FULL of cold food - put it in a day ahead if necessary. Leave space for a bag of ice and put one in just before leaving. You might double bag it to prevent leaking as it melts.
- Leave the reefer door closed as much as is humanly practicable.
- If you stop for a meal, nap, etc. during the hot part of the day, open the roof vents of the airstream to get rid of excess heat buildup inside - the fridge stays cooler if the A/S isn't 120 F inside
- Carry a thermos or small cooler with water/soda in the tow vehicle so you have something to drink without opening the reefer
- on really long hauls, when you stop to rest, turn the fridge on GAS,
- older models, the gas fridge light tends to blow out while traveling, and it could be dangerous around fuel pumps... newer ones will relight. While many people do use gas while traveling successfully I don't see that it's necessary... or smart.
- Of course if you're going somewhere ON the grid, you can easily stop and get groceries when you ARRIVE rather than when you leave.
In the TINY streams like yours, you can't carry that many groceries anyway, and the "bag of ice" could easily be a couple of trays full. Remember many vintage units were literally Iceboxes - You put a big block of ice in, and it melted out through a drain hose.