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That certainly seems like the easiest solution, however I am concerned about whether or not the cabinet will support the weight of the spa when it's on it's side. Plus, I wouldn't be able to locate the leak when it's on it's side either. I think the idea behind raising it up is that you can put a little water in it and actually see where the leak is.I am just not thrilled with the thought of putting the spa up on blocks, crawling underneath, digging out foam and then trying to make repairs.
Might try some dye in the water as it should help you before, and during your dig through the insulation. Also makes pin pointing the leak easier. Never done it but have read about that method before.
This may not be the answer your looking for,but have you thaught about buying a new spa?