Duplicolor bedliner is good stuff. The Walmart brand is Plasticote I think. It works OK, but it's REALLY gummy. Looks like wads of chewing gum when it's sprayed on. It's also more rubbery. I use mostly Rustoleum bedliner from Autozone or Kragen. It gives a really fine sandy type finish like on a steel army helmet.
I'll mask off EVERYTHING that I don't want bedline on with blue painters masking tape. I shake the can for a pretty long time. I spray from about 2 feet away in short bursts. The closer you spray, the heavier/gummier the coating will be. It'll also sag. Further away gives less coverage per spray, but a finer coating. You're not actually painting, so building up multiple dust coats until it looks slightly damp is fine. It won't affect the finish unless it runs.
When it's almost dry, slooooooooowly peel your masking off. If you wait until it's completely dry, the bedliner turns into a shell and isn't soft enough to peel just the masking tape away.
I'd get a couple cans of bedliner, some scrap pieces of wood (old table legs work pretty good!) and practice with your spray pattern and dry time.
