Having a well insulated floor was a project requirement for our Bedbox project. This is an area that you can't easily fix later so we tried to do it right the first time.
The base of our build is like a pressure treated 2x6 sandwich. The bottom layer is PT plywood, then 2x6, then house wrap, then ridged insulation board, topped with regular 1/2" plywood.
The whole base/frame is resting on two built up 2x6 beams which are on cement post blocks. The edge of the build frame was then filled in with supporting stone. The foundation is ledge so it shouldn't sink but we could always blow away. The foundation is basically floating, with no connection to the earth besides gravity. We put our last place on cinder blocks the same way and it never moved. Ledge is a pain to dig in but it's great to build on. Using cable straps might help if we sense the place moving from wind. It is crazy windy in this spot so we'll have to wait and see.