Ventilation may not prevent condensation, if the temperature changes fast enough, especially if the ambient air is very humid, so evaporation is poor.

My take is that you buy a shed, and inside it you build an insulated box with somewhat airtight door, just large enough for the bike, and with a low-power heat source on the bottom of it inside, like a heating pad, or a rod heater designed for the task, or even an old incandescent light bulb, a lot of energy was wasted to heat on those. That should raise the temp enough to reduce the relative humidity enough to prevent condensation.