A traditional two bay antenna mounted outdoors is the best choice for reception of the UHF channels at your location.
Look at the TriplePlay antenna at
www.tripleplayantenna.com. This is a conventional 2 bay antenna built from all fiberglass and composit materials.
The antenna mounts on a simple "J" pole ( traditional satellite mount) and if aimed to 316 degrees magnetic you will recieve your channels 21-28-47-44, and most likly 31.
I have installed this antenna in Rehobeth Beach and recieved all of the channels you requested, and when rotated we also received stations from Philadelphia and Atlantic City.