they don't seal well at all. Our Rage'n never leaked water from the rain but I remember getting some water in while towing in a downpour. We're in So Cal so not a lot of rain. We did spend about two weeks in Oregon one year in November along the coast and it rained a LOT! No leaks.
But if the wind blows just right it whistled and came in around the ramp. You could see daylight at the lower corners, shoved some paper towels in once and that helped. If we still had it now i'd get some water weenies to stick in the cracks.