They aren't RVs and aren't really portable.
Oops, further research says I'm wrong - they are RVIA certified as park models.
First, you've got to have commercial land - not public land.
You probably have to go through the same legal and zoning issues as anyone building a new RV park would have to do.
While they may have self-contained composting toilets - I doubt any building codes would allow a commercial property to not have a sewer system and connections to all rental units.
There are many commercial real estate agents/ companies who could locate a likely property for you to lease. I think 6 to 18 months would be too short a time to recoup the investment necessary to make the property legal to rent the units.
You probably need to check some small business sites and a commercial real estate / zoning attorney. Its a really complex area which requires great expertise.