I used a mixed up a batch of motor oil and diesel for the bed (1" plywood) of my Toyota \GMC (has a 56 GMC bed) and applied 2 or 3 applications, letting each soak in. Then I let it dry a day and allied several coats of...
Black walnut stain mixed in with an old can of varithane sealer.
It took a few days to finally dry but I now abuse it like the garbage scow I use it for.
Leaves, garbage, whatever, it is still holding up well. Well enough I had to drill a couple drain holes to let it drain...