Could it be as simple as finding a good Realtor, buying in a working class neighborhood, etc, and renting it out?

That is one of my worries of going into a class C or lower area.

not to be a debbie downer but I would not use my primary residence for a heloc and then invest out of state.. especially a C or D class property.. too much risk in my mind  also keep in mind Heloc's can be called or frozen thereby putting you in default and you wont know it until after the fact they are not fully amortized loans.

We acquired the deal mostly for the lot, it’s a B class neighborhood in a growing city, on an excellent street. 

The lot is zoned as R2 and currently only has 2 units on it....RV/boat parking came to mind.

Buy 7, sell the lowest two performing ones to pay off the other 5 or trade in for class A properties--lower returns but lower stress and maintenance.   

The big concern I have with this asset class is the control element.

Military housing is at high occupancy on-post, making various home displacements more common off-post in hotels or short term rental homes.Small multi-family homes vary in neighborhood types, but the majority of them (but not all) are in a low to middle class area, raising the chances of getting unappreciative or undesirable tenants.As I mentioned earlier, I have no properties and only watch the market for now.

If the tenants pay rent on time, communication is good, and the property isn't torn up offer the MTM rent and keep the boat sailing. 

The deals I have seen work are larger 4 units $800k+ in class A/B+ areas mainly as those have less competition and atleast my market noth side chicago they still sell at decent real life cap rates.