Have to say mine almost never leaks - said at the beginning of this thread that last summer we had I've 6 inches of rain during a hurricane and the bed was maybe damp right by the tailgate. I'm pretty sure most of the issues are the cover not being closed completely
nope. I wanted mine to work badly. I studied very closely where it was leaking by selectively applying water to it with a garden hose and tracing it. I spent more time studying this than I'd like to admit
I found a few sources of leaks, some of which i could have improved upon but others i couldn't. On mine, from the factory, there was no way the rear seal would touch the tailgate and firmly seal up. No amount of closing would get you there. I assume i could have disassembled and reassembled it and got that length setup properly and i was prepared to do that.
There were also two spots up at the front that leaked aggressively. These were the biggest source of water as the flow was high enough to drip onto the wheel wells and splash everywhere in the bed. At the front of the roll up cartridge assembly there are two areas that make contact with the front mounting L-beam and that have a little rubberized coating on them to act as a seal. Well, seal they did not. The design was such that water could bypass that seal, and arguably I could have shot some silicone up into the gaps to seal it up.
There were also leaks along the side which i felt were fairly minor but over time did accumulate a fair bit of water.
But there was another critical design element that i couldnt do anything about. The way these things are supposed to work, they rely on the fact that for a viscous fluid like water it takes a certain amount of pressure to push water to through a given sized orifice. If you make a small enough gap, it takes a certain amount of pressure to push water through it. So what they do is they design the hinge joints to be very tight, and literally its the viscosity of the water that is stopping it from pouring in and that fact that unless you are in a biblical flood there will be virtually no head pressure of water driving a leak on top of the cover. The trouble with that is 1) it relies on the manufacturing to be really tight (which is entirely possible but not easy), 2) it relies on those hinges remaining unchanged over time (which might be a problem since they advertise that people can carry weight on top of it, encouraging people to flex those hinges and loosen them), and 3) the forward most hinge on mine was not actually flat. When the cover was fully closed, the forward most hinge was actually at a very slight angle, it wasnt flush to the rest of the cover. It tilted in to go and coil up on the roll mechanism, and it did it a little too soon (would have been a better design to not do that until under the protection of the drum). With the forward most hinge not being flat it leaves a wider gap open at the top of the seal, and that one flap leaked more than the others. They all dripped a little bit under heavy rain, but the forward most one was considerably worse on mine. I tried adding a clear wax layer to the cover, because making a hydrophobic barrier at that slat would slow the water ingress. It helped but could not eliminate the leaks.
I took my cover off intending to try to fix these issues. When i had the cover off I realized how much bigger the bed seemed. You are losing 25% of an already very short bed to this drum assembly at the front of the factory cover. Again, not an issue for everyone but I'd rather have a non leaking cover and my bed space back, so I went with an aftermarket. I'm pretty happy with it now, no leaks in torrential rain.
Edit: i will add that one thing was sacrified along the way: the new cover overlaps the tailgate, which is part of the reason why it seals so well everywhere. But in so doing it puts an added resistance to the tailgate dropping. My keyfob release tailgate will not drop on its own now, you have to pull it. It wasnt a feature I really use so I dont really miss it, but if thats a thing you really want to keep the style of cover I installed might not work for you
