A key and feasible amenity that seems to be missing from older properties are package lockers.There are a host of vendors out there and Amazon even has their own proprietary system. 

I help host the BP monthly meetup here in Miami, I will reach out to members this month and find out who is going so perhaps we can organize something.

go talk to a local bank and see what they say

I've yet to not have to replace one except in 1 property that the bank put in thinking they were making it livable and able to put it on the market.

85/15 traditional 15-year loan with local bank How did you add value to the deal?

Small local banks .

Some owners want a higher interest rate than the banks will charge, some match the banks, and others will take a low interest rate.How long will you amortize the loan?

I have looked into lot links as well as the Montgomery county land bank foreclosure acquisition program.

Absolutely, but few banks will loan on a park with no infill plan so that moves your capital from the development side to the MH acquisitions side. 

I made an offer on a house and because I am doing 50% financing, the owner offered to lend the other half himself and be paid over the next 30 years, at an interest rate lower than what the bank is offering (albeit, not much lower).