If cooling unit is functioning it doesn't matter which energy source is used.....electric heat element or propane. BTUs used in the heating process is the same.
Are your leveling your rig when parking?
Off level operation will disrupt the cooling flow cycle.....causes insufficient cooling, causes accumulative damage to cooling unit (overheats coolant and causes plating out) which is permanent.
How is the freezer section cooling? If it is cold (0-10*F) and food section temps are fluctuating up/down.....cooling unit has blockage.