There are automatic vent openers that you can buy for about forty bucks each.

In his blog about building his new 6x8 HFGH, dewey1945 shows how he applied 6 mil UV resistant plastic to the outside of his panels. I havenâÂÂt seen this idea discussed anywhere before, so IâÂÂm interested in following his blog: Apply the UV Resistant Skin When I replaced my roof panels in October of 2011, I applied a clear marine coating product to the outside of my new panels, before installing them. I also applied the same product to half of a scrap of HF polycarbonate (left over from installing my exhaust fan.) IâÂÂve left it exposed to the sun since October 2011. So far the treated side still looks shiny and clear, while the untreated side has started to look a bit dull and cloudy. Might be a good sign, but I think itâÂÂs still too early to tell if this product really does help. My cost to purchase a gallon of the product was around $100. The company (Top Secret Coatings) seems to have changed their product line since my purchase, so IâÂÂve emailed them to ask which product is the current equivalent of what I used. IâÂÂll post back here as with that info as soon as they reply. ItâÂÂs too bad we have to wait at least a few years to see if ideas like this truly will help extend the life of the HFGH polycarbonate panels. From my reading, folks in southern states with intense sun seem to report more panel failure. The topic hasnâÂÂt come up here at GardenWeb for a while, so IâÂÂm hoping that means folks in other climates arenâÂÂt having nearly as much of a problem. If you donâÂÂt do anything to protect your panels, and notice some problems in years to come, you can order replacement panels from Harbor Freight. The HF panels wonâÂÂt last as long as higher quality twinwall polycarbonate from other supply companies, (with real UV protection,) but they do cost a lot less. FYI, hereâÂÂs a summary of my pricing research from October 2011, for just enough material to replace the roof on my 10x12 HFGH, including shipping to my state: Farmtek 4mm twinwall polycarbonate, approx 10 yr warranty, about $410 Solexx 3.5 mm, (a flexible translucent white greenhouse covering material) about $350 Harbor Freight 4mm panels, $135 IâÂÂll be sure to post back with the Top Secret clear coating product number, so itâÂÂs recorded here for the thread.

I don't know where in Arkansas you are, but if you're not too far from Oklahoma City, you can buy polycarbonate panels at American Plant Products, a wholesale greenhouse supply store not too far off Interstate 40. This is where I bought my twinwall polycarbonate panels, although they're 8mm in comparison to the 4mm HF panels. You might ask if they sell the 4mm panels. Here is a link that might be useful: American Plant Products Wholesale Greenhouse Supply

Joe, in case you didn't see it, Laserfan posted this information recently about a 4mm polycarbonate product now available from Tek Supply: "I notice today that teksupply is carrying 4mm in the (much higher quality with UV protection) PALRAM polycarb. Expensive as all get-out, but here you go. If you look at this page, be sure to download both of the pdf files there as they contain excellent information about both the product and it's application/handling/installation etc. that you will find valuable I'm sure. Link to Teksuppy 4mm page: laserfan" If we eventually do have to replace our panels, I'll at least give a more expensive option like this some careful thought, since I figure it will be a major ordeal to replace the panels in mine (I'll have to empty out the greenhouse, which remains stuffed year round.) I don't want to spend big bucks...but I'd rather not replace the panels very often, either, and I now know the HF panels may well have a limited life span in my climate. Sheri