We are installing a jet tub and due to walls surrounding the area, we had to build up the tub. The instructions call for setting the tub in concrete, but with how high the tub is, it will have to be a huge slab of concrete. Can you support the tub with a stilt-like frame?
I can tell you however that the reference to setting the tub in concrete really refers to providing conforming support to the bottom of the tub. You can set it on a built up wooden floor then use the method below BUT the support floor must be heavily built and able to handle the total weight of bathers, water and supporting mortar bed.
One answer is to lay down builders felt and then a mortar or plaster bed and set the tub down on it while it is wet, then let it harden.