I buy plastic painters drop cloths and just drape it over the machines, let them hang loose so they will breath seems to work for me every winter. I also cover the mill and lathe ways with iso 32 oil and then saran wrap
Remind me please of why you would want to cover a machine?
Ok, I am beyond help then. I guess if I stored them outside it might be a good idea. BTW, It is a serious question. my machines are inside a shop, my humidity is not extreme. I keep them reasonably clean and have not seen any rust in the 4 or 5 years since I bought my first machine. Is there something I should know about care and feeding that I am missing?