Been there done what you propose and most owners are too short-sighted to care about this.Many will agree upfront, but wait until you try to charge that renewal fee and you have to deal with their complaints.

-Proposed Terms.Ultimately the agreed upon terms were $385k with $85k down and a owner carried note of $300k @ 5% interest only ($1250/mo) on a 3 year balloon with the option to extend for another year at 6% interest only ($1500/mo). 

I am specifically talking about mobile home parks in my proposed scenario.

@Jason,What you propose is not possible for two reasons.You cannot mix IRA/401(k) and personal funds. 

What I'm proposing would dramatically increase the number of units available in the area if adapted on a large scale. 

I propose introducing an escalation clause to generate interest and encourage visits.

(Note: 4-plexes would hard to find at that price point)1: What would be the terms proposed to the lender for questions such as…a: Duration of return of capital (+ negotiated fee).b: how/when/how… installation amounts of the return of capital c: What the pros and cons are for buy & hold with respect to returning lenders money plus interestd: Or might buy and hold not be in the best interest nor the best vehicle for such a potential lender?

What would be a reasonable down payment percentage or amount to propose to my family member?

It's good you realize the amount of work that a contractor might put in to his free price quote/proposals. 

@Eric FernwoodEric, do you have any thoughts about the proposed rent control bill winding through the current Nevada legislature session (SB426)?