This is a response to several inquiries, I've gotten on different boards. There are tons of "volunteering" jobs available through many Government agencies. Some are long term others short term. You can at times actually,negotiate your work conditions, length, etc. Also, you can pick up jobs with the concessionaires at National Parks, etc. I talked with a retired couple last winter who ran the park's kayak and canoe concession at Collier-Semiole State Park in Florida, were going to Big Bend NP in Texas for the spring, then work in the Tetons doing light maintainence for the concessionaire during the summer.
In January, I checked and applied for Campground hosting in both the Gallatin and Shoshone forests outside of Cooke City. We recieved offers in both, taking the Shoshone due to last summmer's experences. At the same time I saw that there were hosting positions listed as open throughout the Northern Rockies and Pacific Northwest. There were lots in the Bridger-Tetons below Jackson at that time.
This is a "JOB" with specific duties, we have to clean the vault toilets, clean fire pits, greet campers and explain Bear Food Reg.s. We have two days off, rarely taken, and have to be available in camp on the weekends. We work approximately 2-3 hours a day. We camp for free in our large pop-up, get free propane, weekly 5 gallons of gas for generator, and $15 a day for 5 days a week. (We may clear $1000 at the end of the summer) We could be called on 24/7!! We usually cleaned very early, went fishing or hiking and came back about dark to do the "meet and greet". We act as "the eyes and ears" of the Forest Service and aid visitors in the forest. We have had folks host for a month, then be relieved by others for the rest of season. We plan to host from Mid May till Mid September this year, then may see if we can work out a July/August stint next summer.
The Florida State Parks, for example, require 32 hours of actual work each week. You have a designated sign in time and schedule. I've seen some folks come in and camp free on the Keys for two weeks or spend two months hosting. The workers for concessionaires at some National Parks get paid for their work, besides free camping. Some of the National Park personnel in Yellowstone have housing provided as part of their compensation. I talked with a gal (a teacher) in Yellowstone last summer who picked a different park every summer. I'm not sure how the Smokies work. This is the site for various governmental branches. http://www.volunteer.gov/gov.