Workamper has many resources.. it is also set up as a subscription service, so unless you pay the 40 a year fee, the site is sort of limited. It is the "standard" for getting these kind of jobs tho, so if you are serious about it.. the 40 is a pittance once you get in and start exploring.
Paying subscribers have access to additional forums with user inout on places they have worked and some additional resources for job finding.
They send you daily openings via email if you want, and employers are hip to the site, so they pool their resources through them.
BUT.. you can still get to many tips and tricks without subscribing. They also have a library and bookstore with lots of good info.
The net can bring up other resources as well.. yahoo has several groups, RVers on Wheels is another. Keep looking.
I suspect it is like "real life" tho, and you get gigs by word of mouth or circumstance. I got my summer job simply by expressing a generic interest in doing this full time in the future.. two weeks later, I got a call from the host I was talking to at the time.
Workamper also does Job Fairs on both coasts. Many of the larger national employers go to them (KOA etc) I went to the one in Mesa this year, and was offered positions on the spot. (I am not ready to full time yet, so I declined)