Is it condensation on the outside leaking in, or condensation on the inside of the storage area?
If the condensation starts on the inside, you need to vent the compartment - and in such a way rain doesn't get in.
But I have to question why condensation would be happening to such a degree in a storage compartment. There has to be a source of moisture in the air, and no way for the air to move, such that the compartment walls or lid can get colder than the air inside.
Are you covering the camper, including the storage compartment? That would prevent the air moving and cause condensation.
If the water - condensation or otherwise - is leaking into the compartment, the seals may not be working properly. My Coleman Westlake pop-up had that issue with the front storage cover. I had to install rubber gasket material around the opening to stop water coming off the roof from getting into the front storage trunk. There was no real lip around the opening, so I made one from 3/8" round rubber gasket glued in place.
2019 Flagstaff T21TBHW A-frame (stored in the garage)
2008 Hyundai Entourage minivan
camping Colorado and adjacent sites one weekend at a time