Craig's list is a great start. It's Free. Cancel the old add and replace it every week. Rotate the pictures.
Be very sure of the year make and model and any optionals or additions.
Have the coach ready to drive and get GOOD pictures.
If it has not been run in a year or more, get it registered and insured and take it out on the road. Yard queens go for much less than running - working ones.
Take lots of pictures. Get on one of the free photo sites and put all the pictures there.
CL allows 4 pictures. Use 2 outside and 2 inside for starters.
On you CL page, be verbose and include a link to the pictures.
On the side, collect the tire dates and be ready to knock off for tires over 7 years old if you are asked. If you are not asked, then the buyer is not serious or is very uniformed.
Some people are looking for a very specific RV. The more you include the better are the chances of one of the CL searches finding yours.
Do not be discouraged by low balls. If the offer has not seen it, tell him to come and look and make the offer after has has seen it.
This won't be easy, you will have to work some for your mom's money, but in the end it will be worth it.
Matt - who had to sell his dad's last boat.