Even if you have a spray in bed liner, would still recommend a rubber bed mount. Helps prevent the bedliner get damaged from any small screws in the bottom of the camper while also preventing any of those screws getting pushed too hard by the truck. It just adds that little bit of give and take needed to make sure bed and camper bottom work together well.
I'm a cheap skate of sorts, yet even I saw the advantages and quality of the Torklifts mounts combined with Fast Guns. Been using them for five years without an issue.