Not sure what direction is best for you but I can share how I started. 

I was wondering if a manufactured home would be an economical and profitable solution. 

Either way, run your proposed solution through an attorney. 

These loans do come from banks directly (Fannie/Freddie loans come from the Federal Government) so each bank that offers these types of mortgages might have slightly different requirements. 

Did you ever find a solution for a 3rd position heloc?

If it is a direct lender you are able to work to find more favorable terms because they usually determine their terms on a deal by deal basis. 

Combine that with America’s housing shortage, and the solution becomes clear:We need to build more homes that align with what buyers can afford.

I have a solution that I do myself once a year.Here's one of my best tips: go on Airbnb as a TRAVELER, in Traveler mode.

and some guidance from the FTC is here: https://www.ftc.gov/tips-advic...Simple solution - DON'T.

The way I see it is I am 2 years into the amortization of a 10 year land loan anyway… so it might be a viable solution.