We always use eBay or craigslist. I also used RVT.com once and had success. Part of it is putting up a compelling ad for your RV. So many people dont give enough pictures or details. They only end up getting a portion of the suitable buyers to contact them. If your going the classified route (online or otherwise), I would give this
sell my rv in the classifieds article a read.
We once listed our RV in several places and found it almost impossible to keep track of the inquiries. If you havent done it before I would choose one and stick with it till you get a feel for it.