Personally, I think you'd be in a legal nightmare if you tried renting the units. 1 - you're running a business, you'll have all the legal ramifications to contend with - insurance, taxes (private and business), liability, upkeep, maintenance, repair, utilities. 2 - you're wanting to use public land to set them. All you need is one disgruntled person (either renting or a neighbor) and you'll most likely be getting a visit from some authority person, possible fines or worse! 3 - If you are able to use private land and "rent" the land, you'll have zoning issues, even if it's in the country. Eventually someone will report and the owner of the land will get notices from the zoning board (city or county) they are in violation. Then you'll have to break leases or contracts with your tenants, move the units and could face legal action against you from your tenants.
If you can find a way to get around zoning, insurance liability, and state/federal/local taxes, then you'll probably be OK.
Now, if you're wanting to set one of these units up for your own use, and park it off the grid, you can probably get away with that, just like any other camper parked "off the grid".
You also run another risk. Actually, this is a true story. There's a little "campground" right off of I69 North-East of Indianapolis at the Anderson exit. This little campground consists of several little cottages, plumbed, electric, and actually livable. You can also park an RV there, but the cottages are usually all the most people use. There's a lake (dug out when I-69 was built), and its stocked with fish. You can fish there without having a fishing license since this is private owned and stocked.
A few years ago, people started moving into these little cottages and using them as their permanent residence. Unfortunately, the authorities shut down this little camp site because the people who moved in were registered sex offenders, and using these cottages as their permanent dwelling address. The site shut down because of all the bad publicity, the owners faced massive legal actions, and it was an embarrassment for the entire town of Anderson that this happened. Not to mention that "regular" (families) now quit completely utilizing this facility. I'm not sure what the outcome was, but I think the facility was finally forced to sell and it's now under new owners. It's a sad story ... I hope you really think about these things before getting yourself into legal problems that may be way over your head.