Is it cheaper to use a window unit other 2 rooftops ?

To your question, No it would not be cheaper. Makes no difference if you are camped at a park but because you pay for that elec. As others have said you will need 220v hookup not available at parks that Im aware , far and few between if any! If you are in a place where you have to pay your own electric, then the roof air is efficient. Why mess with the rubber seal around the window or cut a hole in your wall. I personally think a window unit in a camper looks tacky unless its an older unit and a window unit is the only option due to no wiring on the roof for a roof air unit.