Installed the Rough Country liners on my 2021 1500 just a few days ago. Will confirm they are a beast to put in. 20 minutes according to instructions, took me more close to 2 hours from start to finish. The second one goes a faster once you figure out the technique on the first. Definitely have to man handle them and get the left and right completely in up past the curves before getting the top. Twice I was able to get it all end but one lip at the a curve but at thay point its near impossible to push that last piece in. Had to pull the top back out and man handle the corner in while slightly moving the other side to try to get some slack. Attaching some pictures of the finished product and the part you dont want to be at, stuck with 1 lip left in the corner.
The factory flare screws didnt seem very tight at all so that concerned me on how much to tighten them after getting the liner in. I tried to match the factory tightness, maybe just a bit tighter.