"I wonder if renting a power fence hole drill would have been a better investment)."
Yeah, digging three foot deep post holes in South Texas in August is my definition of H-E- double hockey sticks, although it might be a little warmer than Hades itself
Like the old Waylon song say's "Ain't no God in Mexico." I bet there ain't no devil either, since it's just too hot in August down that way for him
As for the wind, I don't have a problem as my bonsai are big. The biggest of them sit on the monkey poles--which have surfaces about 2 feet by 3 feet. The pots on the trees are six inches smaller than the surfaces. Hurricane Isabel (gusts to 70 MPH) didn't budge the 150 pounder a few years ago, but I moved it to the ground after a big gust blew the fence down...
I would secure smaller bonsai, under 25 lbs with either wire, cloth strips (for smaller trees) or those elastic bungee cords with hooks meant to secure cargo in vehicles for larger trees. The cord ends should be hooked to eyelets on the underside of the platform surface. Wire or cloth ties should go all the way over the pot and be tied or joined underneath the
supporting platform.
good luck. Put this off until October...