2.What are the best and most cost-effective solutions for managing this potential long-term issue?

I'm also having issue with no onsite manager, but in regards to insurance. 

Even when I self manage I include pm because it is work and I do not work for free.

I currently self-manage three properties in the Atlanta metro area and have learned a ton through trial and error over the years.

@Luke Spencer I am not on the management side but I can tell you it took 2+ years to fill 300 units at one of our facilities and the other just hit 300 units in 12/13 months so it really depends on the demographics, and local housing market trend, the more people moving in and out the higher the demand for storage.I think if you're looking at a saturated market then the upfront cash to turn the warehouse into self storage is not a good idea but then again, maybe those operators are on back roads ( low visibility ) and don't push google ads well.

That means learning how to vet a manager.

You may make $50k on a flip but have to wait 6 months from list. ( in specific areas - not all of CLE)As a full time investor turn time is hyper important for me to turn my properties and money over as many times as possible in a year.Another example is are you a flipper or a renter.

STR Property management is common and I know a lot of folks doing this.  

My tough today is different than my tough next week.Many new(er) investors struggle to manage their rentals well.

It's best to have a house manager.