Usually I have to tell people that they don't but you, @Adrian S, have clearly demonstrated that you do know Jack! 

I was thinking of a spray foam insulation.  

You'll shave at least a point off your mortgage rate.

I have also seen it installed over foam, I know they use this when they are trying to get a bit of slope on the roof not sure if that is the only purpose for it. 

A $5 can of bee spray foam should do it.

Have you considered shaving your facial hair?

I know you have to shave off $100~$150/mth off the listed rents to get closer to actual rents.

Either way when running the #'s - having one unit rented would make the mortgage payment which is most important.  

You cant tell from my picture but if I shave my face I still look like I am 15 so I used to have to sit across from potential clients and tell them why it was a great idea to let me manage their $10 million dollar retirement. :) Very challenging to say the least.

I am doing my cladding on the outside, with closed foam insulation.