In the past, I've tried used several different rattle-can "rubberized" coatings consisting mainly of asphalt or vinyl. Neither is all that tough. The vinyl is a little easier to work except for some minor blushing issues (like laquer). The adhesion is probably a little better with the asphalt. Neither will dry completely if sprayed on thick, which isn't necessarily a bad property for a fender liner. However, I'm concerned that a thick enough layer of the vinyl (even built up slowly) may crack and allow hidden rust behind the coating.

However, in the past I've always been fixing a minor rub with minor hammering, padded by the original coating, that left the zinc plating intact. All I had to do was coat it with whatever was handy to prevent stone damage to the plating.

Recently I had some major rubbing on a sandy lot, with sand on the sticky tires definitely cutting through the plating. I also did some major hammering. So, now corrosion protection is a bigger issue. I already applied several coats of weld-through primer (first Wurth alu-zinc followed by U-Pol zinc, simply because I ran out of Wurth and can buy U-Pol locally). I definitely like the Wurth primer (even though no welding is involved) better than hardware-store cold-galvanizer paint. Adhesion is good on the Wurth, but I don't know about the U-Pol yet. Adhesion is poor on regular cold-galvanizer.

I'm thinking about trying a true catalyzed polyurethane truck bed lining, but that will be expensive and I'll have to waste most of it. I'm a little worried about adhesion (don't want to scrub the zinc primer too much), and it will be tough to repair if more pounding is needed. Brushing it on would be a big plus.

Thoughts?

I use dupli-color spray on truck bed coating-better than any undercoating I've used. If you need something tougher than that try Herculiner which goes on with brushes and rollers.

What about an epoxy based coating, maybe mixing up a portion of some floor coating kit?

If you have bare CLEAN rust or metal I'll recommend POR15, but you MUST clean the surface first. If you have rubbing issues then that small section should be down to bare metal so just hit it with some brake cleaner and paint (slather) with POR15. Read and follow the directions otherwise it wont protect as well.

http://por15.com/

For road cars, my Dad used to spray the spray-on undercoating, and then, after it had had time to set, covered it with a couple of coats of semi-gloss black enamel. It seemed pretty durable, and the black undercoating wouldn't rub off on you when you were under the car. But then again, we weren't racing these cars.

I had been under the mistaken impression that Herculiner required mixing in a catalyst. It's actually a humidity-catalyzed polyurethane, as is POR-15.

I used Herculiner on the bumpstop area, where the Duplicolor vinyl truckbed liner gets scraped off in even the most careful tire changes with 17x11.

I tested the Herculiner and Duplicolor on the zinc weld-through primer, and the Herculiner was both far more durable and had much better adhesion on the zinc, but as Rob said the Duplicolor is very easy to work with.

However, I'll probably need to do just a little more "fine-tuning" with the sledge, and I already know that a regular wire brush (not knotted) in an angle grinder goes through the Duplicolor like buttter. So, I used it over the zinc for now.

Once I'm finished hammering, I think I'll take the vinyl and zinc back off and use POR-15 (with their zinc phosphate metal prep) instead of the zinc primer as the base coat. Then the choice of top coat won't matter as much.

I've used POR-15 and that stuff is PICKY about surface prep. If you don't do it right it will come off in sheets a year later. I would definitely use their metal prep products. I cleaned surfaces with acetone and brake cleaner even. I'm suprised the dupli-color truck bedliner didn't work. It cured to a nice semi-hard finish for me. The Herculiner should be much tougher. You could always just drive to a Line-X location with your car.

I wouldn't say the Duplicolor didn't work at all. That's what's on there now. However, it will actually peel off the zinc while brushing it out if you aren't careful (had better luck daubing it on with the bristle tips), and it peels off the zinc too easily when dry.

In the test sample and on the bumpstop area, the Herculiner had no such issues. It formed an inseparable bond with the zinc.