We purchased ours right out of someone's front yard so make it visible to passers by and have it CLEAN. I don't mean just "sort of" clean but really, really clean.
If you can park it somewhere that is on the route to a major camping destination - do that. Particularly right around Holiday weekends. Often the trip home is where a person is saying "I'm so over this tent/camper/unit I have" and maybe they see yours and sold!
For listing on CL lots of photos. I'm a serious buyer and I'm not "calling for photos" or emailing for photos" If you can't show photos in your ad I assume you are not a serious seller. Have clear photos and lots of them. Remove all personal items. I don't want to see your "Best Grandma" throw covering the sofa and needlepoint pillows burying the bed. I want to see it as the manufacturer would have featured it. Please do not have children/pets in your photo. I'm not buying your grandson and your schnauzer. I want to see the rig.