You are not allowed to camp in PENMAR. It is just a very small park with picnic tables and other things in the middle of a neighborhood. The AT simply transits through it.
The place I camped looked like an unofficial camping area, kind of common along the AT. You are permitted to camp along most of the AT, just pick a spot off the trail and ~200 feet from a water source.
No fees.
Look into this: http://www.aldha.org/comp_pdf.htm