I've always used Rhino Liner. I think it is a bit thicker but stickier than Line X. This is good for keeping things put but not so much for shoveling out dirt/gravel. My present liner is 5 years old. Faded but no dents and has had a lot of stuff (iron and firewood) thrown in to it. I also use the standard Ford rubber mat when the TC is loaded. Still my camper has shifted in the front while on a steep sidehill/rough trail. So I had to add 4x4 treated blocks to wedge between TC and sides of bed.
You have been very lucky with your plastic bed liner. Every one I've ever seen has ruined the bed paint, even rubbed holes clear through the bed.