That way you could acquire with hard money, put your own skin in the game via the repair costs utilizing your HELOC, and then refi out and get cash to pay off your HELOC and the hard money lender and keep the property as a rental.  

Got to be careful and really clear here - its not an unreasonable ask - but its a totally different request (and will be challenging) to be requesting capital investment from a partner with zero actual monetary "skin in the game"

.#3 how the deal is structured....do you have skin in the deal and have integrity, or are you going to take my money and run if you end up being in the 70%.

Also do you have to use moisture barrier below?

The issue with hoarders is damage to the property- hoarding can lead to pest issue, moisture issues and other issue that physically damage the property over time and can lead to big $$ repairs. 

The interest rate is about 8.5% but the cash is accessible within weeks and we would only have to bring 10% down for our skin in the game.

Lot's of different ways to skin it.  

More than 1 way to skin the cat. 

I need my own money saved to put my skin in the game.

Roof age and condition: Create a visual checklist to use during a showing for signs of moisture intrusion or past/active leaks and make every attempt to gain access to attic/roof sheathing.