Unless you are going to show the truck and keep it under raps or garaged with no-one touching it I suggest you make your own planks. I am a cabinet maker also. Shrinkage, movement, and moisture is going to happen in a truck. Especially, if the truck will see the outside environment. You will also throw stuff on it, scratch it, and probably hammer nails into it to haul stuff.
I have a truck (or trucks) and wanted a truck. I went to the oldest lumber yard in Dallas and bought yellow pine. It was old lumber. It is seasoned. If you buy your wood at one of the big box stores (Lowes, Home Depot, etc) I would bet that it will be from a tree that is quickly grown and your growth rings will be wide. Again, I wanted yellow pine. I cut it to length and width - then took a router to cut the sides to depth. For the grooves I used a skill saw. Outside the commercial shop with the larger equipment I use hand equipment. I have a steady hand. I believe the planks came out a good as any you will pay hundreds of dollars for. I finished them with marine varnish.
All in all, I think the entire project cost $80. It is functional for me. My truck stays outside. But you may be different and want a show car product that will win trophys.
Best of luck.
