There really isn't enough information here for someone to give you a proper answer.What you need to do is calculate those tax savings over the next 5-7 years (or however long you plan to stay in the house) vs. what the interest rate reduction will save you over that time period.

I am under contract on a lake front house but still in the due diligence period - I just learned that it's designated flood zone A.

Make sure if you go into a contract (no option period), you require a substantial earnest money.

@Noah Schulz what does the lease state about payment and what period the payments cover?

If you do go under contract, make sure you have ample DD period and that there are contingencies included so you can get your earnest money back. 

My timeline for turning over vacancies is strictly four weeks, which is the maximum acceptable period between a tenant moving out and the arrival of a suitable new tenant.

Quote from @Scott Trench: Does the math change on using a HELOC if you use the HELOC for a short term period, until completing a cash out refinance on one of the LTR's that I own?

Also, there have been several hosts that have come over from airbnb during that period.

Then, you can calculate how much cash this property(ies) is going to eat over the period you plan to hold it and see if what you can sell it for (less commissions, taxes, etc) will produce a profit.

Thus allowing you to set automatic late fees in case the tenants doesn't pay before the end of grace period.