You don't give your size, but I'm thinking your best bet in the area will be Campers Haven on Old Wharf Rd in Dennisport. The Bass River Trailer Park is right in So Yarmouth, and looks like a nice place, but it seems to be mostly permanents, and I don't know how many spaces they have for large transients. May be worth a call. Also, the Old Chatham Rd campground in Dennis is pretty tightly set up.
Whichever you select, ascertain their closing date. Most CGs in E Mass close right after Columbus Day w/e-- mid Oct.
John & Diane, Fulltimers. RVM103 NHSO
On the road since June '12 with Lincoln, the guard cat.
2002 Dutch Star 40, Freightliner, Cat 3126, 2004 Element