Background Reading:  6-Q: Tub Warp   

Tips:

–With the cover off, crouch down so your eyes are at the same height as the top of the shell, and visually align the front and back of the hot tub shell. Do they align perfectly level and parallel, or do you notice that the opposite side does not align, or one of the corners lifts a bit?
-Peer down the cut edge along the side of the shell skirt in the same way you’d check an arrow for straightness, aligning corner-to-corner to see if it’s dead-straight or if the line sags/droops in the middle.
-also, make darn sure that the pad you intend to place it on is perfectly flat.