I have sailed up and down the Cape fear river for a few years in the Adventure island and have enjoyed it immensely. People always talk about the Gators in the river but I have only ever seen them north of downtown wilmington where the river splits and is alot narrower. I never go up there anyway. The shipping channel can be quite busy and you will see BIG container ships and the like. They throw big wakes but I just have fun with those. As for camping.... I have never done it but people camp on the numerous Islands in the middle of the river. Don't think any one ever bothers them. one in particular called Keg Island (look on Google Maps of the river) has a sandy Beach area on the North west side that has a Geocache, Corp of engineers marker and fire pits and well above tide tent sites with great views of the river. The currents can get weird and the wind can kick up some rogue waves in some places Like the memorial bridge. Just watch the tide tables www.saltwatertides.com
and follow the river zoomed on google earth.