I am a novice with this stuff but could you not install the vent and then if you decide you really don't need it, silicone it permanently?
I found that my vent really made a difference last year even with fans blowing and the door left open.

I think the roof vents are my least favorite part of the Harbor Freight greenhouse. The vents on our 10x12 would not stay shut tight, even when the silly vent latches were in the "locked down" position. Because of our prevailing wind, the vents would pick up slightly, then bang down. Over and over, super annoying. I had to silicone the panels into the vent frames, because they vibrated out. I eventually wired the vents shut with baling wire; I got tired of climbing up on a step stool to mess with them on windy days. When we replaced our roof about 3 years ago, we removed the vents entirely. (I said, good riddance.)

Looking back, though, I probably should have tried investing in some vent openers (Bayliss or Univent) before giving up entirely. As CanadianLori says, I know it would be a big cooling help during our hot summers. Here in the desert southwest, I manage without the roof vents only because I convert the entire south wall to screen in the summer months, and keep the sliding doors wide open, with three fans running (one exhaust fan.)

So I did remove mine, but I stop short of recommending it to others, because I think it does make cooling more difficult. I do agree they are a pain.

mudhouse,
Do you still have those roof vents that you removed? I'd like to add additional vents to my GH, but near the bottom to let fresh air in. If you still have them, can I buy them from you?
Thanks,

Hi newgen, sorry, I don't have them. The vent poly panels were completely deteriorated from the sun, and we have since scrapped the aluminum frames. You could call HF for pricing, though; I bet the framework and panels would not cost a lot to order. Sorry I couldn't help!

mudhouse,
No worry. I just ordered some shutters instead. BTW, how's your GH holding up? Haven't seen any update to your blog.
Thanks,

newgen, the GH is good, I'm getting ready to start the annual fall load-in of non-hardy succulents and cacti from our patios. Sure wish we had another few months of fall.

I never seem to have time to update the blog with current photos; I only find time to respond to the comments and questions posted on each section. Maybe someday...?

I installed only 2 vents with univent openers. They work well and I installed louvers in the front of the greenhouse and the side as well. I am installing a 16 in, exhaust fan with louvers.