(especially panels). Also, if the wood shrinks much more than the paint, the paint can bulge and bend.
One solution to these problems is to keep the temperature down and always use a humidifier.
When relative humidity is very high (over 60 percent), wood can expand much more than paint and cause cracks as well. Another problem that can occur in high humidity environments is mold growth. It feeds on painted and varnished surfaces, as well as leather and fabrics. One solution to these problems is to use a humidifier and fan.
An unheated garage with a basement and attic can be an ideal storage facility. The carriages can be stored in the middle level on a wooden floor, thus allowing temperature and humidity changes to be more gradual. Remember that any dramatic change in temperature and humidity can cause the vehicle’s panels to crack.
The fans (extractors, in roof or wall) can reduce temperatures and improve environmental conditions for storing horse carriages.
Finally, keep in mind that the extractor vents must have a fine filter to prevent any infiltration of insects.