Not the kind of greenhouse you have. You can heat huge greenhouses 100x30 footers even bigger if they are steel framed with double wall insulated plastic with modine heaters concrete radiant heat flooring ect... but your greenhouse is uninsulated and all the heat rises. So itll be the top half warmer but youd need alot of heat dont think eletric heaters would work. You could use propane heaters but thats going to create even more moisture if your plants are covered your better off then the majority of ppl. All my full terms are outdoors and exposed to the elements. My seed plants with the biggest best buds arent molding at all, but my cookies and gelato clones are molding. So i'm seeing mold on 18 plants total out of 42 but the rest of my clones are wedding cake,ice cream cake, birthday cake, mimosa which all have smaller nugs. The worst it about to be over. You may lose a bit to mold but it can easily be trimmed out and if you are covered then you probably wont end up losing much at all. This weather is crazy though so wet and cold. All the hemp farmers are feeling it here in SoOregon. Imagine trying to cut mold out of acres of hemp fields lol