I’m in eastern Washington, which is much drier, so take this in that context. Years ago, I had a sailboat that I stored outside with no cover at all and never had a mold issue. The boat had ventilation, didn’t leak, and wasn’t trapping moisture, so it was fine.
With my tug now, it’s always stored in a building, and I think that makes a big difference. It never has snow sitting on it and never gets rained on, so moisture simply isn’t being introduced in the first place. In my experience, keeping water off the boat matters most, and if you do wrap it, it needs vents high and low.
Hagadone’s in Coeur d’Alene likely has indoor storage, but that’s something you’d need to arrange earlier in the year. Even so, towing the boat about 300 miles there would be a much better option than a 1,500-mile haul elsewhere.