You brought up one of my main concerns in mobile homes.

maintenance can be a valid concern,,,sounds as if you have those bases covered.

If part of the house has no foundation at all - I assume this means the sub-framing is sitting directly on the ground - that would be cause for concern. 

Not much newer plumbing to speak of although my better halfs family is a family of plumbers so that helps out with that concern.

As you are concerned on the stability of the industry workers (quite valid) and of the relationship,  offer a short term (3 or 6) month lease holding over with m/m.

That is only concerning the MLS, it's also important to have a good agent to screen wholesale deals for you as well.  

@Brent CoombsI agree on the concern of over leveraging and crazy interest rates, but the timeframe I plan to borrow is extremely short.  

My concern is both take care of the property and both pay on time, i am unsure if i want to continue renting because he wants control of things and it makes my life stressful BUT he is in the right according to local law.

There are different tax and legal consequences for any number of other types of business structures that may meet your needs.As for your concern with Trusts, they are a different creature entirely.

I certainly wouldn't want a drug dealer, or a user of more dangerous drugs (i.e. meth, heroin, etc.) living in my units, but I'd be less concerned about a pot user than an alcoholic.