Condensation is the result of cooling down air that contains moisture (humid air).
Running the air conditioner removes moisture from the air. That is the dripping condensate you see from your roof.
The longer the air conditioner runs, the more moisture is removed from the inside air and dumped on the ground. However, if you are leaving vents open, you are continually letting in more humid air from the outside. This warm humid air touched the colder surfaces and instantly leaves condensation.
You must seal up your camper by closing your vents.
Remember: the act of cooling down warmer humid air creates condensation. When warmer humid air touches anything colder, it will condense.