Hi Joan,
You're talking about workamping and it's very prevelent out there. Have you logged on to Workampernews.com? They are the number 1 company matching campers and campgrounds. The person who told you to get an agreement before arriving was spot on. Make sure you understand the job, days off, pay, visitor rules, etc.
I'll do my next article on this subject delving into more detail. Feel free to email me in the meantime with specific questions.
Evanne