The reason for the comment about Bronze Age artefacts is not down to the value, its about what they need to been stored. Cars get driven outside, they get wet, they are designed for it! Obviously you want to make sure your not keeping them in a damp place all the time and I totally get that, but as long as it is ventilated and the sun and rain is off them your doing what you need to.
The other aspect of it, which I personally consider quite important, is that a dehumidifier uses a load of electricity, where as a suitable vent in the end gable if far more ecological. From the sound of it, while an extra vent would likely be a good thing, your garage like most is not air tight enough for a dehumidifier to be appropriate anyway. You will just be sucking water out of the air in the garage, and dipping it the otherside of the garage door (directly or otherwise) to come back again!
While some may feel talking about environmental impact on a sports car forum is silly, but I don't feel it is.
Daniel