Heck of a web site, by the way.
I'm expecting the delivery of a 7ft x 7ft hot tub shortly, to be laid on a new 16 sq metre patio area (probably Bradstone oldstone) but I'm unclear as to what strength of sub base I should use. I mean, the tub won't be moving about (like a car on a driveway), but it will weigh a lot when full of water and my wife.
Hot tub supplier will usually provide spec for base, as Tony says 150mm compo slab. We usually sit tub straight on reinforced slab and pave around it, but no good if you are going to ever move it.
Don't forget cable for power supply, if to run under paving.