My insurer is Erie, for everything including my umbrella. 

And you avoid things like damaged properties (guest insurance from airbnb or prop manager themselves cover that), evictions, collections, etc.   

There is title insurance issued at the time of purchase, so we don't want to invalidate that.

Is it a stable long term strategy?

Find yourself a good team who builds ADU's has a project management team and of course has all the licenses and insurances to protect your property.Quote from @Michael Adamo: Hi BP Community,I’m exploring adding one or two ADUs to a property I own in the Miracle Mile area, near 3rd Street and La Brea in Los Angeles.

Keep in mind that many of these cheap homes are selling for less than a third of their insurance replacement value, which really means that the land has negative value - let that sink in.Most buyers who can actually qualify for a mortgage will get a PA for $200-300k and desperately want to upgrade their life.

We just need to figure out how.I’d urge you to look at the insurance business, which has a great deal in common with real estate.

Well if Proper won't insure it, many others won't as well.

You can try to go after their renters insurance, but since you don't have proof, you're probably not going to get anywhere.

How much are you qualified to borrow and what will your monthly costs be for mortgage, insurance, taxes???