I charged them $300 a piece per month.  

Three pieces of advice @Richard Oglesby...I would certainly agree with @Michael Woodward on reading the Millionaire Real Estate Agent. 

I have seen many speculative pieces over the past day on what is causing it, but it is just that - speculation.

now that's a bit of piece of mind. 

:) Now let's see if I've done the alerting piece right ;-)

Tell people the skills you have and your goals and what pieces of the puzzle you have, you have some capital you have construction, you have FSBO resale or you can always get a good realtor, you don't have a deal or skills to get one and you probably don't have full financing to make a cash offer with no contingencies.Get your financing in place, are you going all cash, are you using hard money, are you going to partner with a money partner, are you going to get a fha owner occupant loan?  

I shouldn't miss any piece of that.

You have given two bad pieces of advice in this single post.  

After paying off your original note of $100k, you have $60k tax free in your pocket and a new 30 year note to show for it (with higher payments than you were previously paying)With a HELOC, all you are doing is taking a piece of the equity spread you have in your home.

With only seven lots and two thirds of an acre I also would asked the question if this is a true permitted mobile home park, or simply a small piece of land the owner has added more and more mobile homes to over time.