Those of you with toppers, caps, etc. on your pickups...

My LEER was allowing water to wick inside from the headliner being exposed to the rain. The dealer just trimmed it back to solve the problem. I added the tailgate seal that sticks to the body and that stopped 90% of the dust.

Can a passenger see the water coming in around the tailgate while you're driving? Could the water be coming in through the front or the sides? Is the topper sealed against the rear of the cab? If so can you open the back window a bit to allow airflow into the topper to break up any suction at the tailgate?

I get a few dribbles around the Leer Cap but not much.

But I've also put foam tape all around the tailgate opening (sides and bottom) and under the plastic tops of the side walls to seal against dust. There's also a few seams and holes in the bed that can be plugged. Think that helps.

The Leer Cap itself seems pretty tight. Its door has a big lip over the tailgate, and door's sides and top are sealed up when it's clamped shut.

EDIT: and the cap has foam tape under it where it rests on the sides and front of the bed.

I also have a Leer and have not had any leaks. I installed an aftermarket rubber/foam gasket for the tail gate. Depending on how level I park. I may get about a cup of water in at the tail gate where the gasket I installed has a gap. I never get any water when I park level or while my truck if moving down the road. Sometimes we get 3 or 4 inches of rain in a hour and I see no water in my bed.

I have a Leer as well and do not notice any leaks. It's interesting, because I can see some daylight sometimes around the tail gate. The leer door does come down over the tailgate on mine, so that helps.

My ARE cap does let water in. I am not sure exactly where. I do know that we sucked in dust last year running the back roads.

Since I have a drop-in bed protector, I put a rubber bed mat on top of the bed protector. The water stays in the bed protector, and things on the bed mat stay dry (and do not slide).

Thanks for all the hints. I will look into the gap seal tap - it might work. The truck is a 2500HD DA CC 4WD and it has a rounded over tailgate, so the flap on the topper seals great. From inside the topper, looking out, I can only see sunlight along the vertical edges of the tailgate/truck bed so that is why I am assuming the water leak is there.

My truck primarily tows a gooseneck horse trailer, but we have the topper so we can run errands in the rain and pick up bulkier stuff then the tonneau cover allowed us to. And the Velcro on the tonneau was pretty much shot, so it wouldn't stay attached anymore, and needed replaced.

Since putting the topper on the GMC, it has proved priceless for "hotel" style family trips, as there are places we go to visit family where pulling a 43' toyhauler is just not feasible. No sense having to park the TH at a campground 30 miles away when the GMC will fit perfectly in the driveway while we sleep in an extra bedroom... BUT! It really sucks when rainwater soaks EVERYTHING in the bed of the truck. There has literally been water sloshing from front to back in the bed, it leaks that much. Not fun.

This one does, none of the others has leaked.

Mine leaks real bad.
I just don't put anything near the back that I don't want to get wet.

Jack L

I have a Leer topper on my '09 Silverado. Absolutely no leaks.
I believe '9 was the first year that GM made the edge cover of the tailgate with a nose on it. I did not like it, was told that the bottom edge of the topper back window would sit on top of it. So I had it replaced with the previous style that fits flush over the edge of the tailgate. So the rubber flap attached to the window hangs over the edge of the tailgate.
Not knowing which style you have, maybe there is your problem.
I also installed foam tape to close the gap between tailgate and the sides , but that was more to keep the dust out.
Alex