I've got a 1.5 meter (approx) length of concrete sewer pipe (unused!!) about 300mm diameter with a flanged end. I keep eyeing that up and down with the idea off rebo-ing into to my big slab and filling it with concrete with a mount flange on top. It's heavy enough and wide enough at the base to be almost stable on it's own. Run a couple of 2"-3" downpipes down the middle for wiring & data etc.
But I'm not serious enough for a big mount yet. But one day, one day .... if I ever get the AstroPhotog bug ..
