I think you are asking for it if you intend use green wood. What kind of wood do you plan to use? Some wood does better than others outdoors than others. Red oak is one that does pretty bad for what you are doing and treated wood is one of the best. As far as the finish you can expect any film finish to wear off pretty quickly so if you paint it you will have to retouch the paint pretty often. I have a trailer that has a treated wood deck and I painted the trailer but the wood deck I just used Thompsons water seal.
If you do use paint I would use an exterior primer and a oil based enamel and paint all surfaces of the boards before putting it on the truck.