Holy gay-names-for-box-liner-paint Batman!
I did a light sanding of the box on my old '86 and then used the $7.00 an aerosol can undercoating stuff. I think it was 7 cans total. Easiest and cleanest way to do it is get a helper and pull the box off.
Could hit that cheap crap with 3500 psi pressure washer or a hammer: it stood up and never flaked off.
It's all in the prep.
Or, you could go the best, easiest, cleanest, and cheapest solution possible: 4x8 sheet of plywood. Beat it like a rented mule and just get another sheet. My $30.00 "box-liner" is in it's 3rd truck. Pull that sheet out when you go to trade 'er off and the box looks like new.
Contrary to popular belief, an applied box-lining material will not increase the re-sale value of your truck. It's just stealership talk for "we want to soak you for another $1500.00 on your purchase". No different than back in the day when they used to up-sale undercoating, or the rest of the B.S. "protection package" stuff.
Just yanked the sheet out for a wash-job in this photo, still looks brand-new, don't it?
