Oh so you pulled the plastic grommets out. I was thinking about that but just left them covered for the moment, was thinking about leaving them and not bothering with the locks. The extender was very tight on mine too, I just backed the bolts off a little and that helped. They are still tight but not as tight as i would like, I will keep and eye on them.
Yeah, it's kind of sloppy IMO if you just cut holes and leave the grommets behind the bedrug. Then you just have holes or slits in the rug. Putting the plastic caps back over top really finish it off to look OEM. I'll get some pics of mine all reinstalled, I think you'll decide it's worth the little extra work to reinstall them over top the rug. Plus they also help keep the rug in place at the tailgate and really secured in. They're a little tricky to remove, but some blue tape to keep from scratching the paint, a putty knife to start lifting the edge up, then a flathead screw driver, and they pop right out. Feel and cut the holes, then a deadblow to pop them right back in fully clipped and seated over the bedrug.
I don't use the locks either for locking the extender in the bed, but when I flip it out on the tailgate I will. And I originally left the side bolts not as tight so it wouldn't clamp against the bedrug as tight, but then the bolt heads would rotate, and typically only rotate on the loosen direction, and not on the tighten direction, so over time they'd eventually really loosen up. So I tightened them till they wre locked in place to not rotate. I noticed factory put lock-tite on them so I'll probably add a washer under each side, and lock tite them on reinstall.
On the BAKflip, it rattles against the cab when driving while open. I found that out when I moved some furniture yesterday with it open and locked up. So I took two pieces of that half round rubber they provide for shimming and stuck it to the bottom side of the BAKflip where it touches the rear window when all the way open. Worked as a nice bumper.
My Bakflip came with 3 pieces of rubber about 1' long each, taped to the bottom of one of the panels. About 3/8" wide and 3/8" thick. At 1st i wondered what the heck they were, then I realized. Those aren't for shims, the f150 version has the preinstalled shims. They are for the panel against the cab when open. When its open against the cab, it's just the hard metal hinge against the rear window, and driving with things moving it would scratch up the surround. So I put those 3 pieces of rubber along the edge of the panel where it would touch the cab, 1 in the middle and 1 on either end, and it worked perfect. Now it's got cushion for any flex and vibration to not harm a thing, and when the cover is shut they're on the bottom side so it's in the bed and you never even see them.
What is the benefit of the plastic drain tubes for the bak flip? I don't have mine on
So whatever water that runs down into the channel will drain through the tube and out of your bed. If you don't have the plastic drain tubes connected, water will just run into your bed rather than through the tube and out of the bed.