Is it ready for broad adoption?

Just as I would not expect an institutional investor to buy and manage homes, I don't think I'll be doing that with the SEP either.Here's my recommendation:Hands-of investmentf: Go with the SDIRAHands-on (or potentially hands-on): Go with a typical (non-IRA) process

How are fellow investors paying multiples mortgages on multiple properties; especially if they are financed through different institutions?

It has solid cash flow and great tenant currently living there.Can anybody recommend me a bank/credit union/financial institution that can provide me 200K HELOC  (up to 70% LTV)?

The US subsidiaries of Canadian banks are leery of financing Canadian purchases in the US unless the borrower has a significant and deep relationship with these institutions in Canada. 

And the 100+ parks that were sold to PE are institutional grade parks.6000 spaces free and clear is a cash flow monster.

That's true, and that's why institutional lenders can lend you money at 4.5% or 5.5%.

Definitely check out your local rules and regulations, and if there aren’t any yet in your town regarding short term rentals, research whether or not there are any in the works as a lot of towns are adopting similar rules to my area.

My plan A to keep the note (notes) for 2-3 years and than sell to probably an institutional investor. 

You cannot purchase the property personally and then assign or transfer to your IRA.Any self-directed IRA vehicle will likely take 2-3 weeks to establish, largely due to the timeframe involved in moving funds from your current institution to the new institution.