OK, hardly an expert but I have an unheated garage. Maybe ventilation is the issue more than heat? I went from 6-degress F and snow to 40 and rain this week with no condensation in my "garage". But it breathes a lot. It is on piling with a planked floor. Sucks when you drop a drill bit, but the ventilation is good. But here are some other tricks to think about. Buy some two or three inch aluminum vent tubing (stove pipe) and wire a light bulb socket in the center of a four foot length. Put in a 25 watt bulb. If you buy two 2-foot lengths, you basically put the socket in the end of one, then push them together so that it is left in the middle of the length.
The heat will cause air to rise in the pipe. Now, find something to throw over the bike, like and old blanket. Cut a hole in it and stand up the pipe through the hole so that the bulb is below the cover. The rising air will circulate the air to help keep it dry and the bulb will keep the temp up a bit. Be wary of course of fire hazard but the bulb doesn't get so hot that you should be able to lay your hand on the stove pipe without any problem. The light bulb chimney has been used on boats here in Southeast Alaska for a long time to prevent moisture in closed cabins. The old trollers did this a lot. Now days people instead spend a lot of money on dehumidifiers. Such is the way of technology.
Russ