That means the -ve cash flow will be my housing costs. 

Not to mention the ARV would get a little bump if you were interested in cash out refi on the property along with a rent raise. 

This is very similar to adjusting DTI if the borrower owns cash flowing rental properties in addition to their primary residence. 

I am helping a client who is also a Veteran to do this exact thing right now; at first he wasn't sure he wanted to move twice to make it happen, but when he realized he was going to basically get a cash flowing rental property for free(no money down) he realized it was an easy decision.

It has a strong potential for cash flow and property values are steadily increasing.

I am already preapproved and could move on to something else that would not cash flow nearly as well.

I have found that the return on a SFH STR in those areas is minimal in comparison to other assets as they require a large down payment, but with management taking on 18-30% of rents it's much more difficult to manage.  

I would like to save up for a down payment on a duplex. 

The house hack approach makes sense otherwise.Think about cash reserves.  

Lenders usually look at the debt payment coverage ratio within a certain amount of time.