Using multiple HELOCs to buy for cash..anyone done this?

[Blake Morris]

I have a HELOC on my primary mortgage. Just refinanced it to another bank. The bank I have my original HELOC from sent me a payoff letter that says unless I request it in writing my line is still able to withdraw until 2023 (paraphrased). That line was for 25k. I refinanced it to another bank with 25k line because they have a lower introductory rate.

so...what if I refinance to another bank next year who offers an introductory rate and bank number 2 does the same as the first one by leaving it open where I can draw from it.  then, ill have an available 50k to pay cash for a rental at prime rate versus paying higher interest with a 30 yr fixed.  the payment would be interest only on both lines but id pay more than just the interest.

50 k plus 10-15 I would throw in anyway for a down payment is plenty for my niche. no closing costs.  no appraisals.  cash in hand.

anyone done this or do any of you see anything I am missing?