I have had a slide in liner before, and I liked it very much except for what it did to the paint in my bed. The problem I see with spray in liners, is that they would not be dent resistant, or scratch resistant. I used to slide axles and engines and all sorts of stuff on my slide in liner, I might get a few shavings off it, but nothing went through. I think If I was dropping loads of rocks on the spray on, it would dent the bed of the truck and scratch off the spray on coating. Has this happened to anyone?