Hi, I had major problems with a Conquerer 1998 where both sides had to be replaced under warranty. The problem was the longitudinal seems didn't have enough overlap and water entered by capillary action.
I think I would check the sealant around the door frame as a first option and replace it if necessary. Then put a dehumidifier in for a few days and check with a damp meter. Higher readings MIGHT show where it is coming in but water can track and give a false indication of the entry point.
Good luck, Glyn