I would not approach it from the standpoint of I want to build container homes and then look for a site, I would have a site and think about what the best use of it would be and if it happened to be container homes then go for it.As John mentioned above appealing to the masses is the route to success here IMHO

Does anyone know of a reliable site or resource to check zoning laws for Airbnbs or STRs in general?

Think of it like a dating site in that its purpose is to just bring the interested parties together, but if love is to bloom, it will take some work.

Applicant is ok to show me in person his account information on his laptop, but doesn’t want to put his user name and passwords to those sites into RentRedi application.

Most of my guests will go in and tell the restaurants /shops that they are staying with my glamping site for 10%.

HUD publishes the Median Fair Market Rent on their web site for the entire country.

I would make a site visit to where they live now and see how they treat the current property.

It provides links to each county office's sites for when you're doing research. 

It is usually a tenant moving to a new area, because of a new job and they just want to be done with their trailer.I have had the disgruntled situation come up when I stopped using the on-site maintenance man and made him pay full lot rent like every one else.  

Look at Listed properties, open houses, for sale by owner (FSBO), wholesalers deals, any on site auctions you can find, and look at as many deals other investors own that they are willing to show you.