Thats what I did, cept I used cabinet grade since I have alot of that on hand. Sealed it with epoxy (also have lots on hand), and bolted SS strips down on it. Did not rout grooves...wanted the strips above the wood for protection.
Toughest thing would be sealing the edges and holes well enuf to prevent water getting in and swelling / warping plywood. Also with oak ply, you don't get the grain variation you see with individual planks. Veneers are pretty thin surface. Make your own planks. I bought 1 x 6 & 1 x 8 dressed Oak at a wood worker supply place for around $ 125.00. Grooved the edges with a table saw.
If you are trying to do this with as little work as possible, just throw the plywood over the top of what is there. If you have to take it all apart to put the boards in, and you are just using the truck for a driver or a "not for show", just get some 1 by's and cut them to fit. I believe the instructions can be found here at the bolt or at Mar-K (look in the upper left of this page). I just used some good construction lumber and used a good UV resistant deck finish on mine. Replacing the boards as they were from the factory will eliminate a ton of squeaks and rattles too. http://www.mar-k.com/bedwooddimensions.pdf