I need to form up a 9ft x 9ft concrete pad for a hot tub. From what i can tell, everytime i go to the local lumber yard, every piece of 2x's have some kind of crown to them. If I'm placing a hottub on top of the pad, the pad will not be level based on the formwork having crowns to them. is there a better way to create the forms without worrying if the pad will be level for the hottub?