I would not recommend mounting the L-Track (O-Track, S-Track et al) in the bed. The sheet metal in the bed is likely to bend if you ratchet your load down with straps.
I actually saw a pickup yesterday with an aftermarket track system, and their truck bed was bent towards the front of the bed...
I'm coming over from a Frontier as well and found this post looking for the same solution. The truck bed in the Ranger doesn't seem to have sufficient mounting points to place a similar setup in the bed. Even the floor probably won't work. The ridges in the bed seem too close together. I didn't...