I've volunteered for Habitat in the past...........as an Employer/group or a general Community volunteer..........
The RV Habitat for Humanity group is called.....Care-A-Vanners......generally two-week gigs with some camping benefits......here's a link to this years builds:
http://www.habitat.org/cd/rv/schedule.aspx
Habitat is based on the big group experience.............they provide the stable, recognized umbrella under which the total build progresses from start to finish
Attempting to do similar volunteering on a smaller/individual scale is fraught with problems.........As you may know the building "code" generally allows you (unlicensed/handyman) as homeowner to do most projects on-your-own-personal house......Try that on a friend's/neighbor's/or needy individual's property and you can be seriously SLAPPED by local building officials if you don't have the necessary permits and license.......
Also in-this-day-and-age.......the unknown guy living in the van can be viewed as suspicious and/or even dangerous............I'm not happy with that but all we can do is prove them wrong......I'd expect to be able to provide a "clean" Police record
In my own past my BIL was a long-time Quadriplegic.... A NASA computer analyst.....I originally built out HIS camping van to include a sliding bed so he could travel long distance NOT "sitting" in the WC...engineered with a removable Hoyer lift mounted inside the van to lift him up and into bed.....SLIDE the bed........this way his family could still function in the van while traveling
So a "Preacher" in the extended family would call and inquire if I could HELP another person in need........small projects to adapt households to a allow a handicapped person some measure of comfort........clean-up the laundry room electrical hazards.......build a small ramp.......pour a larger concrete ramp........build a wheelchair accessible "desk"........BATHROOM accommodations..........open tight door jambs.......special light switches........All under-the-radar
..................NOMADS is a faith-based RV group of the Methodist Church
Just today..........new member Solari posted about volunteering at homeless shelter food banks.......in the TRIBESEED post
YMMV..........I'll keep watching for more doug