Castaways - we've stayed here a few times. Very nice campground with great amenities. It is on the sound and has a great view of Assateague Island and Ocean City in the distance. Very expensive and although it's good for families, it's more geared towards adults than kids (by comparison with next place...) They have their own beach on the sound with their Jackpot bar nearby, and jetski rentals on-site.
http://castawaysrvoc.com/
Frontier Town - Just a few miles on the same road as Castaways, we stay here a little more often. It's also on the sound and has the same great views. It's a bit less expensive, slightly more rustic, and geared mostly for the kids. They have a fantastic water park, mini-golf and western theme show that Castaways doesn't offer. Granted, you can stay at Castaways and come visit FT for the other stuff. Does not have a beach like Castaways, but does have a boat ramp and marina to tie up your boat if you have one.
http://www/frontiertown.com
Fort Whaley - A sister-site to FT, it's located about 20 minutes from Ocean City, but it a little less expensive too. We have not yet stayed here.
https://www.frontiertown.com/fort-whaley/
If you don't need full hookups, a state park might work. The nearest one in MD is 30 minutes away - Pokomoke State Park, Shad Landing area. They have one loop that would probably work and fees are a little less than $40 per night. This camping is "in the woods" so big trailers have to be careful navigating the park roads. I did a writeup about our stay last summer:
http://campdestinations.com/campgrou...-snow-hill-md/
North of OC in Delaware, there is also the Delaware Seashore Park Campground. We have reservations to try it for the first time this May. Fees were reasonable and it looks to be about 20-30 minutes from the Inlet in Ocean City.
Hope this helps.