Rolf,
One of the things that I have done on my CL ads is inserting every city around the community. That way when someone looks for a MH in a city near your park, your AD will come up in the search. Also you can have a guy in India and Philippines post your ads daily so you can Automate the online posting…elance.com or oDesk.com. These guys work for around 1-5 bucks an hour and are pretty smart.
I would also check to see if any of your local papers have an Online website where you can post your MH’s for rent. Ebay also has a CL like site called Kijiji.com which works well too.
Hope this helps
Max