Quarter sawn salvaged oak from a British ship in the Jamestown river would be ideal. Brush on linseed oil to all surfaces and sides. Re-apply regularly. Seriously, just buy the tightest grain oak you can, white oak is traditional when water and weather are factors. It holds up better than red oak. I wouldn't baby the bed, a little wear shows honest use and gives character to your hard working truck. Just like back in the day. I'll be on the lookout for a vintage metal cooler and tackle box.
L43dean-1968 Fj40 LandCruiser,1980 Rn47 Hi-lux Pickup 4WD and 1985 Rn65 ExtraCab Truck 4WD. YEP!