I presume you are trying to do a ‘no money’ down scenario, correct? Couple thoughts:
What is the amount of the wrap that the owner is providing? $20k does not appear to be much but this may be a small park - you can fund that via private lender, credit card, take on a money partner for a portion of the deal.
Have you talked to the seller about this? Why do they need the $20k? Is there a way to give them some incentive to take on the additional such as higher sales price or maybe some additional profit at the end when you sell or refinance?
With that said, does this deal make enough sense to be highly leveraged?
PS: My 2 cents is that if I were a seller and were doing some creative financing I would want the buyer to have skin in the game. Last thing I want is someone with no skin in the game to come in and potentially destroy the place and walk away.