I installed a used TigerRiver Bengal on an existing flagstone patio sitting on a base of 3 inches of crushed limestone. The Bengal essentially sits on 5 cross beams so I lined up 4X4's under the built-in beams with the idea to shim under the 4X4's helping with the unevenness of the stones while maintaining complete contact with the tub. I also laid 1.5 inch diameter sheets of siding insulation, which have high compression strength, between the tub and 4X4's. The idea there was minimal compression of the foam would insure all points of the base would offer at least some support, making up for imperfections in the tub beams (some minimal beam warp when I got it, probably from a less than perfect previous install ) and the 4X4's. The tub is nice and level and without any issues.