If the shelters you describe are along the Batona Trail, just before you get to the fire tower, they are debris huts, similar to the ones Tom Brown teaches his students to build. These where built by students from Pinelands Regional High School, as part of one of their science classes held every year. In addition to learning how to build these huts, the students learned how to start fires with bows and sticks and how to navigate with map and compass, among other survival skills. Sadly, the teacher who taught this class no longer teaches it and I don't believe these activities are continuing.