From vinyl to bedliner... Top question

The spray on bedliner that you buy at the auto paint stores are generally UV stable. They differ from the parts store variety in that it is a 2 part mix - liner plus hardener. Additionally, it also comes in a "tintable" variety that is actually clear and requires some color being added to it. This let's you mix the bedliner to match the truck. I've done a few of them this way and it looks pretty cool.

As far as using it instead of a vinyl top - it should hold up every bit as good as a top plus you'll have the added benefit of something that looks good and is not creating a moisture trap to create rust down the road. If you don't like it, sand it off and toss on the vinyl top.