Rich,
We stayed at the Capitol KOA in Millersville a couple of times.
Nice campground - located half way between Baltimore and DC which made it easy to get to both places. It's also not what I would consider a rural campground. But it's a good campground to use as a home base for site seeing.
We liked it because we were there site seeing and visiting family in Baltimore. So it was convenient and we really weren't at the campground much.
Just wanted to share our experiences. What your plans are may be different that ours were, so you have to take that into consideration.
Hutch