I totally get the concept of keeping the boat on a dry dock and think it a fantastic idea, but what happens to the dry dock itself. It's bad enough keeping the boat in the water for three months with the amount of crud that accumulates on the bottom. With all those cubes and projections/brackets etc. it must be a nightmare to keep clean. Power washing wouldn't do it, anymore than it does doing the underside of boat. I guess the whole lot would have to be dragged out the water, either flipped over (impossible) or dismantled (massive effort) then cleaned.
My point being, are you saving any time and effort!
I must admit, it's one of the biggest problems of my boat ownership, that of keeping the hull clean. Apart from dry stacking, at not an inconsiderable cost, I don't know the answer. Perhaps inflatable air bags that lift the boat just clear of the water