car cover necessary for garaged storage?

[70Sixter]

I cover the -6 with an indoor cover that lets very fine dust thru over time as the car is not driven often.

I bought a heavy duty outdoor cover for the Box and used it indoors for a time. I noticed that even an apparently clean car was leaving dirt on the felt-like material over the fender touch points.

So now the only time the Box gets covered is immediately after a wash, and when I don't plan to take it out anytime soon.

I also run a dehumidifier in the garage as humidity is a problem here.