My husband likes to go for long rides, like to south dakota, and he was interested in getting a tow a long camper for the bike. Does anyone know where I can get a used one?
Try the classified ads in your local newspaper; Also, look at the specialty car-truck-boat for-sale publications found at gas stations, restuarants, and magazine racks.
Advertisements for motorcycle trailers may be found in motorcycle enthuasists magazines. Two such publications that come to mind are "Motorcyclist" and "Motorcycle Consumer News". The ads in magazines will be for new products, but you can garner ideas about what will fit your needs and best of all, once in while, these magazines will test trailer rigs and report on their likes and dislikes.
One thing to investigate is side-car versus trailer for handling and emergency stopping.
Maybe you can seach on-line and find a digital copies of past articles written by these magazines.
One time I saw a smaller road bike pulling a canoe through Jackson Hole, Wyoming. LOL. He used the canoe to hold his cargo. (The cargo was amply secured!) He had to keep in mind how long his combined vehicle was when passing through intersections.