I personally collect a security deposit and get the damage protection waiver for added protection.

A Heloc can never be used as a PITI reserve, or an asset instead its a debt burden and an additional trade line on credit.A Heloc carries a higher risk when it comes to security meaning if you miss a payment even by mistake or for any reason, your scores drop, or your balances start to change your DTI or usage percentage.

Given your experience and strong financials, you have some solid options:Commercial or Portfolio Loan: These are tailored for investors and can help you avoid personal guarantees, especially since you have an LLC.BRRRR Loan (Buy, Rehab, Rent, Refinance, Repeat): Some lenders offer BRRRR-specific loans with funding for purchase and rehab, allowing you to refinance based on the new ARV once stabilized.HELOC or Cash-Out Refi on Current Rentals: Tap into the equity on your single-family rentals to secure funding for the 4-plex purchase and rehab without high origination fees.Each has pros depending on your cash flow goals and timeline.

They should have good recommendations.If you are trying to do the BRRRR Method, or some other advanced method, now it get's a little more difficult. 

While you may need to sift through less serious inquiries, I’ve successfully secured some strong deals and valuable connections through these platforms.

If they are, then the enemy method works.

More secure and stable than an STR (also less competition) but you aren't in the red like you'd be with an LTR. 

However, excessive shifting could indicate that the opener isn’t secured tightly or aligned correctly.

Do you have a way to secure more off-market deals? 

@Joe S.I would say BP does a good job as well as its membersFor example when peerstreet went under people were on BP blasting them because “they did not know” they invested in unsecured debt because they noted they invested in secured loansBut if you read the literature it was clear the investors were unsecured even though the company invested in secured loans (which this structure is not uncommon) - they were called out for this.There are components related to communication that cannot be verified unless posted but most documents and property transfers (like the one I assume is referenced in the start of this post) cannot be disputed.