Similar experiences here. The drop in type slipped around and rubbed paint off plus I lost about 1/2" of usable bed depth. The advantage was that if I wanted something like branches to slide out or if I wanted to shovel gravel out it was the best.
A rubber bed mat was the best for keeping my slide-in camper and other cargo from shifting but did have to be taken out and cleaned under regularly. At least it is possible. If you get a spray in penetrated it will trap water and accelerate rust.
After market spray in (Line-X) works well for most things. The factory spray in for my F150 is only about half as thick so it ways less and takes less space. It hasn't been penetrated yet but seems a little more slippery than the Line-X. It cost about the same, maybe even a little less than Line-X but I didn't have to mess with the install and put it on the same bank note with very low interest. In my area sales tax on the truck is less than for regular retail items so I saved a little on tax with the factory install. The install was a big thing since I don't live near a Line-X dealer.