About the only way I see to do that is have the insides of the bed sprayed with bedliner either at a shop or with a DIY kit. It would probably be best to do that with the bed disassembled or at least without the wood and bed strips installed. I think I'd mask off the angle strips (at least the horizontal part where the bolts go through. It would be difficult to figure out where to stop the bedliner on the front panel and top edge of the tailgate because there's no real defining line like on the bedsides (where the sides angle out.) With the bed painted beforehand and then prepped properly, it would probably work OK.

Moving your thread over to Making a Stovebolt Bed where it'll be more on topic.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.