HELOC for Downpayment scenario

[Kelley Cock]

Looking for input on whether this financing idea makes sense. We have a primary residence and one STR which we've owned for a couple of years. We have about 350k in equity in our primary residence and are considering using some of that for a down payment on another STR. The areas we are interested in (Coastal North/South Carolina) don't have as many opportunities that fit the scenario of rehabbing for instant increase in equity. I'm not sure how this fits with our idea of using a HELOC to tap into the equity. We would obviously be shooting for a best case scenario but we're also purchasing based on this investment being a home we would eventually use half the year at some point so we have some specific needs as well.
Hopefully this question makes sense. I’ve learned so much from this forum in the past couple of years. 
Thanks,

Kelley