Old D1 rebuild/repair

I got an old Dimension One spa as a flip tub. It was originally installed on unsupported gravel by an above ground pool, and over the next 15-20 years it settled, the gravel sank into the mud created by splashing kids in the pool, and the bottom frame rotted away. That's why I don't recommend gravel.
Fortunately for the owner, D1 makes a full-foam spa and the rotted wood did not destroy the spa.
The owner tried a diy frame rebuild but botched it and ended up with an unlevel, partial bottom...

Old D1 rebuild/repair