My first cab over camper

You'll get all kinds of suggestions for all kinds of reasons and lots of personal experiences for all those reasons. It would depend on the match of your camper to the height of the height of your bed tasks on the truck, depth of the bed, what your planning to use for tie downs, anchors and just plain personal preference. We have a heavy duty spray in bed liner, Reflex, that was applied when our now 10 year old dually was new and it still keeps the camper from sliding around any and has prevented rust. A bed liner can get sand between it and the bed and scratch off all the paint. Some period use rubber horse stall mats, others build up a wooden frame, some use heavy duty house foam insulation material. You'll just have to check around with folks using different things and use what works for you. We wouldn't use anything else but that's just us. Good tiedowns are one of the most important purchases, Hapijack and Forklift being the most frequently used I think. We have Happijack and like them fine but it was an economics choice for us. They've been around for many years but that also is a personal experience and preference. Good luck and happy campering!