The tower is help in place by cement pillars that extend about 4 feet into the ground. They are connected by cross sections that are also underground, and a 4″ thick slab on the surface. The entire mess is tied together with rebar. There is rebar in each pillar that is tied to the bolts that attach the steel tower. The subterranean cross members have rebar that ties into the rebar in the pillars, and the slab also has rebar that is tied to the pillars.
The steel tower has 4 vertical legs that are made from 2″ square steel tubing with 1/8″ walls. The diagonals are 1″ square steel tubing. Everything is welded, and the 4 legs are welded to 1/4″ plates that are bolted to the concrete base.
The deck on top of the tower is constructed of salt treated pine. I just wanted a platform to which I could screw or bolt all of the panels. The closely spaced 2x4s also provide some protection for the back of the solar water heating panel, which is backed by a somewhat flimsy insulation board.