As long-time RV owners, Dan and Virgie Brown saw little reason to stay in one place during retirement.

The couple usually spends about three months a year on the road, traveling to different sites that they volunteer at through a group called NOMADS (or Nomads on a Mission Active in Divine Service).

Road trips can get expensive, though, requiring a few tanks of fuel per trip and commercial RV parks charging between $35 to $55 a night. But once they're on a volunteer site, they can get free parking and their only major expense is groceries and eating out.

In the past five years, the couple has helped fix up a small church in Texas, helped families rebuild after Hurricane Ike and made home repairs for needy families in Florida.

"We are planning to keep going as long as we can," Dan said.