Flowerlady, I haven't dealt with a HF GH, but I don't see any reason why you couldn't cover it with plastic film instead of the panels. You would want to use actual "greenhouse film," which is UV protected, not just the cheaper type of plastic sold at places like Menards and used for drop cloths and such. And the insulation will be less than the twinwall panels, but I don't think it makes a whole lot of difference in our northern zones. (That probably depends on how you are actually utilizing your GH.) I'd suggest using "wiggle wire" (aka channel lock) for attaching the plastic to the GH frame; however, by the time you buy that and the GH film, it might actually be more cost effective to just replace the twinwall panels.
I hope someone with a more definitive answer will chime in and offer some advice for you! Maybe
@Subarctic or
@Moonshadows ?
