I built a special garage about 20 years ago to house a minor car collection and double as a shop. I'm in Houston so a dehumidifier was first on the list. I installed a small central air unit that is controlled by a humidistat. I also installed a central a/c unit to heat and cool but I keep the range rather wide, heat comes on at 65 and cool at 85. The dehumidifier keeps the shop cool and dry (humidistat set at 55 percent) year round. The a/c unit rarely runs unless I manually set it to a more comfortable level. Were I to do it over I would only have extra heat for those cold days. Here in Houston the dehumidifier runs almost constantly so the shop stays cool and dry all the time.
I am near Chicago, in the winter i set the temp to 52 but higher if I am working in garage. If the gas heater runs long it gets dry as a bone so I actually run a humidifier to keep humidity at least above 25 - 30%. In the summer I use a dehumidifier set to 50% that runs when the A/C isn't on.
I store mine in a heated and secured garage. The heat makes all the difference in the world. I live in Western, MA and no humidity really saves the paint. I have been doing this for the last four years. Every spring the car starts up on the first try. I would like to add a third bay and when I do it will be heated.