Recommend cash for keys here (like you already tried) and getting them to sign a termination of lease.If the lease period ended and they are on month-to-month typically you have leverage (depending on what your lease says, or local laws) to end the lease at the end of the month given prior notification.

I started calling other mobile home parks nearby, to get an idea of comparables.

You may find that you can rent a much nicer condo compared to what you would pay on a mortgage for the same number.

MTR is less hands-on compared to STR so that would help with the guest follow up situation. 

Most off market purchases cannot easily be comped with mls properties that comparatively have no risk and are in much better condition).so …Pay for a fixed fee mls listing with the property already under contract.  

I also just generally compared to the 1% rule. 

You should think about what you would offer with regards to your competition and compare rents.

It is normal to get cold feet but the main thing is to do the best due diligence you can do prior to going under contract-  "Pre-DD". 

Quote from @Emory Clayton: I'm confused as to how to screen Sec 8 tenants compared to regular 'market rate' tenants.

Since they can't do each property individually, they use comparable sales to make broad generalizations to determine percent changes.