My thought is to use a HELOC for the down payment on a new property (20% down), then once I acquire it, do a cash-out refinance to pay off the HELOC while keeping my original low rate intact.

The thing that would deter me from this location is a background rate of appreciation of 3.12% and low school ratings.

I've seen lot rents from $150 per month for low end trailer park trash, $350 to $450 for higher end parks depending on the amenities offered.

Parking is worth more than money down there in OB.....And I am pretty sure that your $$ numbers are low, about 50% at least.

You capture the paydown, appreciation, and low payment.

I've seen as low as 9.99% on a bridge loan.For DSCR, I remember the days of 3.5% being the floor. 

I’d love to hear advice from seasoned investors.

If you're locked in at a low interest rate, it might be worth keeping.

With most products their is a place where this makes sense, but in my experience there is only 1 with this product Right Way = Pretty low credit score and cannot qualify for a traditional loan to access the equity and you need the cash fast Wrong Way = Any other reason than the above. 

Biggest lesson would be to have refinanced when interest rates were low and locked in a fixed rate for longer terms without a balloon payment!