I don't know how relevant this is for your application, but my buddy had a 80's Chevy with a cruddy bed and what he did was cheap, fast, and worked.
He sanded all the old paint and surface rust out of the back, then got two gallons of this thick tar like stuff designed to coat beds, and applied it with a paint brush.
The end result is a bed thats nearly indestructable and definately water proof (because when it rains with the tailgate up it fills up like a pool!) and his final cost was about $80.
He liked it so much, he did the floors in his '91 Astro cargo van that he uses for work AND his '90's full sized van he uses to haul his bands gear around in.
Last time I talked with him (just before I moved) it was still as rock solid as the day he put it in (going on 5 years).
Now I don't think i'd do that with a classic, since if you're handy with a router, a quick trip to the lumber yard would put a new pine bed in your truck for about the same kinda jack as the self applied "rhino liner" would.
