Consider your credit score and history to determine your eligibility for traditional or creative financing.

It sounds like you are looking to use Traditional IRA money to purchase a rental property?

If you finance the second property with a traditional loan, you can pay back your HELOC and use it again. 

I am bypassing price labs for MTR completely and charging monthly / airbnb and fixed on Furnished Finder because I found that pricelabs does in fact prove difficult for pricing MTR. 2.

Traditional 30-yr mortgage with 20% down.

Gets deeper from there, but that's the high-level.My goals included being work-optional well before the traditional retirement ages tied to retirement accounts, so therefore the places I put my money needed to afford more flexibility. 

Unlike traditional rental properties, where tenants can easily move out, mobile homes are harder to relocate.

If this is your first investment altogether, I'd opt for a more traditional, simpler purchase. 

You could rent out your current unit and buy another house hack, or even convert the whole property into a traditional rental.

I wondered if SF route might allow us to secure better terms at maybe a 4% interest rate for a few years on the funds not rolled into current $150k potentially assumable mortgage -- and in a few years we could roll into a traditional mortgage.