Assateague has 2 campgrounds, one with electric, one without. I've never stayed at either, but I have visited friends at the one with no electric. It is MISERABLE there. No shade, no electric for AC, no views of the ocean (dunes), large flies...
The non-electric loops of the State Park do allow generators (and the National Park may also) except for quiet hours (10:00PM - 7:00AM, IIRC), so there are some A/C options. No shade, so if it's really hot, it can be rough, but if the forecast is mid 80s in the day & 10-15° cooler at night, as it often is, it's pretty good. There is usually enough of an ocean breeze that bugs aren't a problem, but perhaps I've been lucky in my 3 trips in the last 2 years. It's true the dune blocks the view of the ocean from the campground, but walk 100 feet from many campsites over one small dune, and you have a great view - just ocean, no bridge, no road noise, no buildings, and very few people. Just a few dozen campers in space that would have thousands up in Ocean City.