I am working on 8' long pine boards that are 8/4 thick. They are rough and need to be squared up. I have a planer but need some guidance. I know that I can set the boards on another flat surface, shim them up then run them through the planers. What do you use for that flat surface taking into account how long the boards are. I would think that using any wood board would flex due to the length, defeating the purpose. ANy suggestions would be appreciated.