If you have a garage with a thin roof with no insulation, a concrete floor and generally a cold atmosphere, there are obvious a few areas you need to address. Mine is in an insulated garage which has a loft above which is insulated + my gas boiler helps to keep the temperature up. There are many sites that can help, but obviously the type of garage reflects how easy it is to sort it out. I personally would not want to spend loads on my car and then leave it in an atmosphere that undoes all the good work I have put into the car during the summer. During the winter weather permitting, I take my car out and run it for a long period to dry out the exhaust. At this time you can open all doors remove mats and check all surfaces for dampness. If you garage a car that is already damp I think you are helping the process of condensation.