A temporary market imbalance, combined with cheap borrowing costs (ultra-low interest rates). 

I do some that aren't, but have that in mind that you will be selling for cash, seller financing or on a much higher rate with a mobile home specific lender (higher rates).

Terms are usually 5-10 years fully amortizing in the low-mid teen's on average.They are basically taking a pledge against your future cash flows, similar to an MCA, but with rates from 11-16% fully amortizing on 5-10 yr terms, so payments are not nearly as ugly as an MCA, but similar concept.If they're a TPO or Broker for the same company, the program could be real.

I found out that the seller is very motivated and is offering ALL types of creative financing options with rates as low as 3.75%.

If the cap rate is breaking even or above interest rates it most likely would make sense, taking into account that in five year period interest rate have a higher possibility of coming down than going up. 

If you'd like to hop on a call to discuss the Charlotte market (where your property is specifically), the rate you currently have it listed for, etc.

Or like now when the ROI on bricks and mortar is so low because of interest rates. 

Low closing costs, with minimal documentation and competitive rates.

Interest Rates: The Trend is your FriendSo do we know where are interest rates headed from here?

The HELOC loan will not affect your first line of credit interest rate.