Is that factoring in the HOA costs?

There's always the possibility that they can go up a significant amount based on a number of factors that would really compromise cash flow.

I have a 210K interest only HELOC untapped with a $0 balance and a rate @ 3.75 and I'm looking to do a refinance on some of my other properties and wanted to get a sense of how that would factor in to my DTI. 

That's a matter of long term strategy to avoid ever increasing insurance rates due to hurricane risk factors.  

Based on the BP Calc, I can make $40k with nearly all holding costs factored in if I buy at $330k.The comps on the high side are $600k and up and all have 4-6 bds.

Normal real estate appreciation, the kind agents and homeowners talk about, is dependent on a lot of factors.

Factoring in for weather (something we don't have in socal) Is a necessary step in the due diligence Nevertheless, for my long term landlording goals, I do believe that this will work.Thank you.

Another factor is what you are willing/able to manage.

The income the property generates is the key factor if a bank can qualify.

You forgot to mention that, the most important factor