So in my infinite wisdom (or stupidity) I am attempting the repair myself. If this does not work, I am returning the costco (and taking apart part of my deck).
I added two ~7" 2x4's between the PT wood frame at the bottom of the tub and the underside of the shell where the stress is present. I then sprayed a couple cans of wide gap foam spray into the area. I hit around where the added 2x4s touch the underside if the shell.
Then I drilled small holes at the end of each crack for relief. Then, I got an acrylic tub and shower crack repair kit....mixed that stuff up, and applied it the cracks. Waiting for that the dry, sand, finish.....then refill.