First, and most important, a huge thanks to all who posted instruction on this site to enable us to comprehend the HFGH literature. I couldn't have built my 10x12 without the explanations.
Now the disaster, and a warning. I finally got mine completed on Thanksgiving weekend. By way of explanation I used 4x6 pressure treated frame for the foundation. I built the greenhouse exactly as designed, except that I added 2 aluminum angle iron cross members. I was afraid that any snow load might flatten the roof if the walls pushed out. It went together with no major problems (other than having to undo and correct numerous steps due to the poor diagrams in the instructions).
On Friday, 12/1, we had a major front blow through. 20 miles from me they reported a tornado. I suffered straight line winds of 50-60 mph. The greenhouse didn't survive.
According to my wife, I was at work, it was doing OK, the the doors began to bend in. She tried to tie them together, but with no lock mechanism there was too little support. The doors bent about 6-8 inches (measured when I got home) and allowed the wind inside. The panels on the leeward side began blowing off, but the windward panels had nowhere to go and to whole frame went down. Twisting and breaking as it went.
It wasn't a total loss. The foundation didn't move. Most, if not all, of the panels were recovered and are in amazingly good condition. About half the framework will be reused in another project. The greenhouse will be rebuilt using wood for frame, and the HFGH panels.
After pricing aftermarket double wall panels, I figure my loss, not counting labor, was only a hundred bucks or so. (After pricing just 4 mil panels the kit may be worth buying solely for the panels, but that is another thread.)
Is the HFGH worth buying? I still think so. Does it require additional reinforcement based on your location and conditions, absolutely. Would any greenhouse kit have survived these winds unscathed? I don't know.
We lost no trees, no animals, no other damage, and for that I am truly thankful. (I did lose a cold frame because the ends were open for ventilation. Others that were closed survived.)