Good question and I too have been wondering so I did some further checking around. Here is what I learned from Theresa and also the volunteer building.

As mentioned it's based off of the prior years work
You need to put in 60 hrs.
Even with the 60 hrs the chair person that you report to when volunteering has to agree to it
It's for basic camping only. No water / electric. If you want water / electric you pay the difference.

I'm not sure if there are other restrictions. No one person seems to have the answer on this. I wish it would be clearly posted somewhere. Hope this helps.