i did make my small, temporary, ground rack out of wood, and i did worry about warp, but so far so good.
if i was to make something similar to the one linked, there would be no wood. i was just using that as an example of a 'non-single post' setup. i really would prefer a single post, but it just takes so much concrete for one hole...2-3 yds is too much to mix myself for one pour.
i found a chart for 'recommended foundation size' for certain square foot of panel. 90sq ft of panel they say 48-60" deep x 24-30" wide (square?).....that seems like nowhere near enough to me! i can only get 4' deep due to high water table.
i did a forum search for rossw and traxle, nothing much found...i'll try a search around the net.