I used a realtor that specialized in rehab properties.

Many months of costly vacancy, local market rent & resale deteriation, special assessments, property taxes and maintanance fees suggest a quick sale would have been the wise thing to do 2 years ago.

At my brokerage they specialize in STR management.

Is the line of credit different from refinancing the home that is free and clear? 

Assuming you go the HELOC route, another option to reduce your costs assuming you have decent credit is to look at credit card balance transfer promotions.Back in 2003-2004 I had HELOCs on my investment properties and interest rates were increasing.

Bigger Pockets is a great place to find a tax accountant specializing in real estate taxation.

A colleague of mine specializes in brokering Fannie/freddie commercial mortgages.

I'm not an loan officer, but I know some banks locally like ORNL Credit Union have offered a 0% down conventional loan product.

So keep that in mind when using a special lock system. 

Funding for mobile homes and abandoned parks can be tricky, but there are definitely lenders out there who specialize in these types of properties.