Millennials who have no interest in cars or the loans that go with them and want a simpler, more affordable way of living are buying these homes. Retirees are also looking at tiny homes when it's time for them to downsize, or as a second home.

"When my kids moved out and my husband passed away, I wanted to let the memories go and start a new life," said Janet Millsap of San Jose, Calif. "I wanted to travel but I also wanted to have my stuff. A tiny house was my answer. I travel to some great campgrounds, but one day, I might want to buy property and settle in again in this little place."

Millsap, who rents her permanent home, paid $35,000 for her small abode on wheels, and financed it with a home equity loan.

According to Forbes, tiny homes are not cheap. They typically range from $200 to $400 per square foot — much more than the average new single-family home, which was priced at $97.09 a square foot in 2014, according to the Census Bureau. And the cost of tiny houses doesn't include any land, so how can credit unions get in on this movable housing trend?

The website The Tiny Life says that 68% of tiny-home owners don't have mortgages. But the remaining 32% need someone to finance the cost of their small shack.

"Tiny house lending would certainly be new to Self-Help, as it would be to most lenders," said David Beck, policy director at the $650 million Self-Help Credit Union. "We would certainly consider the loan, probably unsecured or perhaps like a car. I imagine we would treat it like a manufactured home — unsecured unless it is set on a property."

The average cost of do-it-yourself construction of a tiny house is $25,000 in material, according to The Tiny Life. It's a different story when you buy one from a builder. Tumbleweed Tiny House Co. priced its 117-square-foot "Elm" model at $57,000, which is $487 per square foot. Canoe Bay's 400-square-foot "Escape" model can approach $124,000 ($310 per square foot), depending on the options chosen.

Credit unions can offer an RV loan to members who are financing a tiny house, but the house must first be certified by the Recreation Vehicle Industry Association as an actual RV. Many of today's tiny home manufacturers are obtaining this certification to make it easier for consumers to finance their residences.

Unsecured personal loans are another way to help your members and your bottom line, and there may be other creative ways you can help members finance their small homes.

"This trend is good for the ecosystem, and I can only imagine good for credit unions," said Rob Rios, 31, who recently built his own Tiny House and financed it with a secured loan from $1.63 billion Public Service Credit Union in Denver. "Most people who want a tiny home aren't into big banks, so credit unions would seem like the perfect choice for a loan."