Hi everyone thank you for your input,
I always wash the car and push it back in, garage door a roller shutter and I was looking at installing insulation on the joists and space above was going to use as storage.
I don't have any Ventilation, could install maybe two fans, 1 for out going and other for in coming, not sure what's the best place.
I could easily install a small radiator if it helps, maybe keep around 5c ?
A dehumidifier maybe a bad idea as i do have leather seats could dry out?
Car is put in around November to around April every year, been doing it for a few years now, just got some spare time over next few weeks to sort out the garage.