Just curious about it, I googled "northern virginia rv storage" and got lots and lots of hits. The one I was really interested in was the Bull Run RV Storage, which for an oversized space is $222 per quarter, so $888 per year for jurisdiction costs (Arlington, Fairfax and Loudoun and the cities of Alexandria, Fairfax and Falls Church) or $238 for out of those areas.
Holly Acres in Woodbridge has storage for $71/month or $852 per year.
Gateway Storage has several different lots there in NOVA, but they don't list their rates.