The other 3 were month to month and left willingly without trouble once noticed since I allowed a month longer than the minimum notice period, offered a small amount to help with relocation expenses, and returned 100% of security deposits.

Take the maximum security deposit.  

For example in South Africa the law requires that when you sell a property the money has to first be deposited in a South African bank.

., rate of return on deposit rather than fully asset value.  

Perhaps thats how they have become so rich, by holding lots and lots of DEPOSITS with bids.Do they even have agency with the owner of what they are auctioning (ie the bank that has just foreclosed on the property or whatever)?

If you can afford a $15k "SUMMIT", you should consider instead, affording it as your deposit on a REAL deal (but before you buy, you can post your numbers-analysis right here to bounce your ideas off - just like you have with this Thread)!

If you have a great deal ask for a high amount non-refundable deposit e.g $10,000 people with money and are willing to do deals will pay.

Even though this tenant was Section 8 they have to pay the full Security Deposit along with their first months rent. 

Do you need to dig into the HOA's finances and find out how much went into insurance, how much went into utilities, repairs, maintenance, improvements, then spread that across the number of owners in order to figure out how much of your $300 per month went where, and roll each items back into their respective "slots" to see if they can be counted towards the three safe harbors? 

You also need to separate out the estimate items that are tenant damages that you can deduct from the security deposit; there is probably some time limit during which you must return the security deposit, and with that you would provide the itemized repair bill showing the security deposit deductions.