We got the F1 BakFlip a few weeks ago. I went back & forth with Morrey at BakFactory Outlet, trying to find out if the F1 could be mounted without removing or modifying the bedrails on our '11 Laramie. Bak said I could mount the F1 without an issues by leaving the OEM bedrails in place. ........ Not quite
I did have to modify the rear bedrail mounts
(the black plastic bases that slip into the stake pockets) by trimming a groove of 1/4" high by 1/2" wide (with a utility knife) to allow the BakFlip mounting rails to fit under the bedrail bases and flush against the bed while maintaining the spacing between them all of the way to the tailgate (keeping the rails parallel). The BakFlip mounting rails cleared the front bedrail mounts with no problem, but not the rear, so they had to be trimmed before installation. That added about 15 minutes to the installation, which I did myself in about an hour. I ran the drain tubes through the plugs in the front of the box.
I've had the F1 on for about three weeks now, and it stays pretty dry inside. I'm assuming it will be waterproof when the rubber seals settle with some time and sunlight (which has been a rare commodity here this spring). The nicest part of the F1 is that I can lock items in the bed - under the F1, and not worry about anyone stealing anything when I leave the truck unattended.
It's better than a soft cover (more secure, and allows much quicker access to the bed), and much more convenient than a cap or hard tonneau.