The tub I ended up getting is quite large and "wet" weight is over 7000lb. (MasterSpas MP LSX900) I didn't take any chances. I excavated, put down 1' + of compacted gravel,
installed a pretty extensive rebar cage consisting of #4 and #5 rebar, and 4000 PSI concrete. Yeah...it's probably overkill, but that's how I do everything.
Nick B
Middleton, MA