This was my only attempt at a home-made pier mount but it was highly successful.
Concrete base fashioned by hand, in situ, on a tiled rood terrace. A few sheets of newspaper placed on the tiles first to stop the base adhering.
A length of 6" drain pipe pushed at right angles into the wet cement, allowed to dry and then filled to the top.
8" diam 1/2" stainless steel plate with four drilled holes to support the final 8" diam mount plate, plus one central hole to secure the lower plate to the concrete filled pipe. 4 x 6-8" bolts/nuts secured the two together and provided an exceptionally rigid 'cage'.
The 'cage' was to allow access to the mount bolt underneath the Vixen SP GEM to secure it to the top plate and allow easy removal. It depends what your existing mount requires.
The square base was very stable and easy to shuffle around by one person - or lifted by two, if necessary. A round base would not have been so stable. I welded some fixing points on the top plate that gave polar alignment to the mount in Dec, so no need to re-align.
