The mechanics don't change. You take a chunk from the line, drop it on the rental's principal, and route the property's cash flow back at the line balance. What changes is the cash flow feeding it and the paperwork underneath.
Rental income isn't a paycheck. A vacancy, a tenant turnover, or a water heater takes a month of net cash flow off the table with no notice. So the chunk has to be sized against your worst three months, not your average month. If the property clears $600 a month across a good year but went negative twice, plan on the negative months.
Lenders treat this differently too. A HELOC on your primary residence is easier and cheaper to get than one on a rental, where rates run higher and loan-to-value limits run tighter, often 65% to 75%. Some households chunk a rental using a line secured by their own house, which works, and it also means a vacancy at the rental now threatens the roof they live under. I don't like that setup unless the reserves are deep.
The interest side has a tax angle. Interest on borrowed money generally follows the use of the funds rather than the collateral, which can make it deductible against rental income even when the same interest wouldn't be deductible personally. Those tracing rules are specific and they require records showing where the money went. I'm a licensed insurance broker rather than a CPA, so take the tracing question to your tax preparer before you count on the deduction.
One thing separates a rental from your primary residence: you can sell it. If the chunking plan runs into trouble, an investment property is an exit, and that's a real advantage over running this on the house your family lives in.
Start with one property and one chunk. Watch a full year of vacancy, repairs, and tax bills run through the line before you scale it to a second door.