Use a Bed Liner. They are easy to use if you have an air compressor. Like paint or anything else it will scrape off on the rocks but does not chip like paint or powder coat. It can also be touched up as well. I have used Duplicolor for mine on the Scrambler (there is a thread on here some where with pictures). If you don't have a compressor the Duplicolor comes in spray cans as well (bought at AutoZone).
There are others out there. Some are, Upol Raptor and USC Defender Pro. All 3 can be done with an undercoating gun and air compressor. The last two sell a kit with the gun included. Upol sells a clear that can be tinted to match a color and black, Defender Pro (Black) is paintable over it .
A friend of mine used the Defender Pro (black) to line his tube inside and underneath, rocker guards and painted over it (I do not know how well the paint over will hold up to chipping he has not had it done long enough to know yet), inside and underneath the front inner fenders. Sprayed on real easy, with about the same effort as it took me to use the Duplicolor, but I had to go buy a undercoating gun Kit ( under $30) to do mine as I just bought the qt cans, not sure if Duplicolor sells a kit with the gun or not.