I don't have a HF greenhouse, but I don't see any reason why you couldn't use the poly sheeting. (and yes, there is a special type that's UV protected, made for greenhouses; it's generally called "greenhouse film." It's pricey compared to buying the regular plastic sheeting at a big-box store, but the stuff that isn't UV protected only lasts one year - even here in the north -- and the "real stuff" should last at least 4 years. Here's an example:
http://www.greenhousemegastore... )
You might want/need to add some wooden framing to the metal frame, for fastening the poly to, or you could consider using "wiggle wire." Or, possibly you could fasten it directly to the frame somehow -- maybe someone else can offer some advice in that department!
Whatever you decide to do in terms of covering it -- be sure to anchor the structure down securely!
Happy gardening
