Wouldn't you know it? The day after I post a review on the Harbor Freight Greenhouse I just installed in our backyard a storm system with strong winds comes though to give it a test. I spent most of the evening worried that I would be wandering around our neighborhood searching for plastic window panels. Fortunately that fear did not become a reality but the greenhouse did not come through unscathed.
One roof panel detached itself and ended up landing a few feet away. This tells me that my initial concern over the clips not holding the panels on well was well founded. The winds were very strong last night but not the strongest kind of winds like we usually get in March. The panels definitely need to be secured better. Screws with washers to be used as spacers are one option. Caulk will also help to serve as a glue of sorts that can be a backup for the screws.
I'm fortunate that only one panel came off and that it wasn't damaged. If you live in a high wind area be prepared to secure the greenhouse with additional methods as soon as you install the panels. Looks like I'll be heading to the home improvemnet store to pick up some things!