I have a waterproof cover and a damp. unheated garage. Am I better with or without? The answer didn't seem to be in the winter setup thread.
I’d say that using a cover will prevent dust and debris from landing on your bike, but it will trap moisture beneath it since it’s waterproof. You should expect to find mold on the seat, airbox, and depending how long it’s stored, even on the electrical tape.
Air needs to move. Even your damp and unheated garage will see temperature fluctuations weekly and without circulation, the air beneath the cover will cause the mold. You could run a portable dehumidifier and just plumb the line to the outside. The cold won’t hurt the bike, but cold moist air will. You can get a decent unit for less than $200 to do up to a 700 sqft garage.
I am from Seattle, so I am a dampness expert.
Our house is plenty warm but we'll get mold in the corners of the house if we aren't vigilant (behind water heater, in closets, etc.
Your problem is thermal bridging, not vigilance. The cold, moist air outside draws the warm air inside to it. Then it condensates on the interior wall because likely there’s no vapor barrier installed and insufficient insulation. Simple thermal dynamics.