Hot tub platform

I'm moving my hot tub to ground level and, after looking for deck designs, found an interesting one. This was proposed way back in 2000 on one of these newsgroups, but no comments and the poster is no longer reachable through email. So I thought to re-propose here for comments.
This design takes into account the weight distribution of a hot tub. The weight is mainly in the center, in a 4- 5 ft square, and on the side walls. So using lots of double joists looks like a waste of wood. How about building a normal square frame, but have only two diagonal joists. Viewed from above, it would look like an "X" in a box. This would sit on five 6-inch concrete piers, four corners and one in the middle, where the diagonals meet. I would then use either 5/4 decking for the floor, or maybe some PT plywood. The original proposed using single 2X8's for the joists, but I'm thinking of doubling those.
My other option would be a gravel bed. But my problem is that there's a slope of about 12" over the 8-ft span. I don't want the gravel bed sliding down the hill. Might be an interesting slide if I'm in the tub at the time, but not worth the effort. Digging a level 8X8 X 1+deep hole, even if it's not that deep at the lower end, might be more work. And then I still have a 12-inch high gravel mound at the end. So now I need a retaining wall. The deck looks more attractive by now.
So thanks for any thoughts on this.
-Marc
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