Hello.....
Don't know if you tried it yet, but we've had good luck selling/buying things on "craigslist". It's a free site to post on and it's widely read.
www.craigslist.com
On the right side of the page, click on your state.
On the next screen, click on the city nearest you.
On the next screen, (which will look like the first screen), make sure it says at the top of the page the city name you clicked on.
Find the category you want (rvs) and click on that.
You can read ads by clicking on their subject line.
Or to post a free ad, once you are in the category you want to post in, at the top right of the page will be the words "post". Click on "post" and follow the directions.
You are also allowed to post up to 4 pictures for free in your ad.
Good luck to you in selling your rv.