"In order for your Hot Spring® spa to operate properly, and the internal plumbing to drain completely, the spa must be level. If the spa is to be installed on an uneven, or unlevel foundation, shimming of the spa is required.
NOTE: Due to the large size of the Vista® and Grandee® spas, Watkins Manufacturing Corporation requires that these spas be
installed on a level 4- (10.1 cm) thick concrete pad or structurally engineered deck and NOT shimmed in any manner."
Since the rest of the pages focused on shims, I missed the second line of the section. Hope my oversight helps others.
Thanks.