You know, in my mind I had thought that Brad and Jenny's trailer was painted after the truck bed liner went on (okay, now I'm going to have to check
Edit: Okay, I looked at their Picasa album, and the (limited) captions say "We used Durabak truck bed liner," and " it took three coats/three gallons and went on beautifully" So it does sound like they did not paint separately, Donna, you are right.
PS: Kim, I would think the shine retention would depend on the paint. For example, a two-part LPU such as Awlgrip can remain shiny for decades, whereas a simpler, one-part paint such as Brightsides will have much less long-lived shinyness. As to how well they adhere to the truck bed liner over time - that I can't say. And of course you wouldn't get the same "reflective mirror" qualities on a rough surface.
Given experience with "non-skid" surfaces on boats, I would wonder about it holding dirt and/or being a pain to clean. Would be interesting to know how they like it after some experience with it.