I don’t know where you are, but here in Wisconsin the deep freeze would have killed all the pests. If you don’t have a natural deep freeze (winter!) I would suggest a you make use of an artificial one! Wrap your windmill in cloth, then in plastic, sealing it as best you can. If possible, make a hole in the wrapping just big enough for a vacuum cleaner hose, reverse the air flow in a vacuume cleaner and suck all the air out. The plastic will collapse around the structure. When finished, it should just take a minute or two, then seal the hole. Then very carefully pack the windmilll onto a trailer and take it to an indoor freezer plant. We brought about 5o oversized objects from years of outside storage to our local meat locker after explaining that the object was sealed. We kept it there for a week or two, then brought it home and let things slowly thaw out. I understand size may be an issue here, and time also, but I hope this is helpful.