I suggest you think along the lines of forgiving debt over a period of time subject to the buyer keeping the loan in place, an early payoff simply reverts back to the original amortized loan amount.

Have you actually seen credit lines being offered against non-primary residences without seasoning periods?

I show the seller basically three options, 1. they can sell for cash and pay the cost to sell, which is about 10% of the value of the house, 2. secondly they could rented out and wait for appreciation and there's knocking to be very much principal paydown, and 3. lastly they can offer the property for lease to own, somebody moves in and pays their market rent for period of time, works on their credit rating and their ability to borrow money, and then pays full price and also pays closing costs.

I am in a due diligence period on a park which cashflow-wise is a great deal.

Use a higher escrow amount and shorter DD period

If you look at a list of properties on  hudhomestore.come you will see this info under "listing period". 

But yours may be an area tied to issues like oil prices, so the holding period could be through a few cycles (think decade(s)).... 

This move was discovered accidentally and the comment period had only a few days left when the groups mentioned above had to frantically push other things aside to get the comments in within the commentary period. 

sounds like you are like most and need a local mentor who assists you and gets paid as a JV to your deals for x period of time.  

But what I'm struggling to understand is, once I find investors, how do I manage to pay them back, plus interest, in a relatively short time period?