This is a picture of the sled jig for surface planning. It was featured in an article in Fine Woodworking. I made mine a little over six feet in length and 10 inches wide. It is a little heafty when a piece of raw oak is laying on it. However it runs through my Delta 12.5 planner with no strain on the cutters
You lay your wood on top and adjust the wooden wedges to to stop any rocking motion.