Propane or genset for refrigerator when on the road

Most people use propane. The generator will consume more fuel running all day with no load than the fridge will consume propane.

As a very rough rule of thumb, a typical RV fridge uses about a pound of propane a day operating on gas. A gallon of propane is a little over four pounds. Your 100 gallon ("water capacity") propane tank holds 80 gallons of propane, or somewhat over 300 pounds of propane, or something approaching a year of fridge operation.