There are Millions of RV's and Trailers that are collecting dust...
... and they could be collecting money. AirBnB has made a nice opportunity for people with second properties and investment properties to earn extra cash by renting them out at a daily or weekly rate. That's great, but not a lot of people have that extra property just sitting around unoccupied... but each year, millions of people buy RVs and trailers that sit around 50 weeks a year. Many of them are in their driveway. Close, where they can keep an eye on it... unlike a rental property or renting out your place while you are on vacation... only to come home to a trashed house.
Of course, starting this business would be a risky proposition because AirBnB could just add another tab to their website and you'd be out of business. If you were crafty though and went to RV associations and signed up a bunch of people before launch... you could be a nice acquisition target for AirBnb.