Most RV refrigerators will run on propane, electric and some even run on 12 volts (battery power). So be sure to have the rental place show you how to switch from electric to propane and 12 volt.
The propane lasts a long time unless you use the heater a lot.
Your goal will be water and battery conservation while boondocking. The generator can be used to recharge the battery or batteries. Ask the rental what the average number of days the batteries will last if you conserve usage. It should be 2 to 3 days.
Read through the posts to learn about battery conservation tips as well as water conservation.
The refrigerator should only be run on 12 volts while your are driving down the road to prevent the battery from dying.