I found the best thing to do is get a drop in liner, and get a huge bucket of grease and grease the entire box then set the liner in.... not only will it prevent scuffing, but it will prevent rust, and when the sun hits the liner depending on the grease, it will melt and seep into all those crappy body glue joints and help stop some rust... I did it on my 1990 ranger which are terrible for box rust, and I when I took up the liner, it was dirty grease but under it was still good paint...
I agree with Wayne on the spray in liners... they look nice, but they hide problems and like he said if you wanna keep the truck forever, there are better methods....
the only reason my truck is still a truck is because of oil guard and krown... I can't stress enough how important it is to help a truck last... you could even go as far as to drill a couple holes in the side of the liner, and tell the krown guys to blast oil in there every year when you get it re applicated...