We would like to start using Cozy or Zillow Rental Manager for our rentals to collect payment and screen tenants etc.

Perhaps you can collect an additional deposit for utilities to raise your deposit monies.

Im pretty sure just about every park in the state doesn't allow you to rent them out, so selling with owner financing and collecting some interest is the best option ive seen. 

Seems the state will even try to collect the transfer tax if you move the property to a trust.

Many renters have pets (many have secret pets too) and some owners will just not notice secret cats (for business purposes), just to keep collecting rent from the resident so they don't move.

If the work wasn't done to code, you could end up paying repair costs, building code fines, and suffering loss of rental income, since some jurisdictions don't allow you to collect rent until the building's defects are cured. 

I'm interested in what others have found to be the best approach(es) for improving the chances of collecting back rent.

As for the short sale aspect only, you may not be able to collect a commission, as the buyer, depending on the investor/Servicer.  

In order to successfully do so, I am trying to collect some money on the side to purchase a home in France.

The problem with investment properties is sometimes seller's really aren't terribly motivated to sell, because since they are collecting rent each month (assuming there are tenants in there) then it's not a huge deal if they don't sell for their asking price.That being said, sometimes I tell my investors: what's the worst that can happen?