Unless it's a really high end place, monthly rates are typically down around $500-750/month, so more like $5-7.50/hr.
If you are really volunteering, it may be OK because a free site is a side benefit but not the reason you are there. I could see being a greeter/info person at a visitor center...cleaning toilets isn't my idea of volunteering.
For the paid jobs, the pay may be horrible but I would disagree with you get a W-2 for money you never got to see. You saw it but it was provided in the form of barter. Reality is at the pay rates we are talking about, you are paying next to nothing in terms of income tax anyway.
We've thought about similar but looking at going to a tourist area (say Mackinaw or Yellowstone) for the summer. With a small full time population and a busy tourist season, they have lots of summer jobs. Get a job that pays cash and then get your own campsite. If they offer a campsite, it's on top of being paid. We'd be looking at it as a way to qualify for heavily subsidized obamacare before we hit full retirement age. If you hit around $25-30k/yr, the subsidy makes insurance dirt cheap. If you make too much the subsidy goes away.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV