Seller financing contract

I have a park owner willing to sell me his park and carry financing with a reasonable down payment. Does anyone know where I can get a good contract with general language in it, I’ll customize it from there and have my lawyer look at it.

Right now I want to bind the deal while I do due diligence and make sure I want to close the sale so all I may need is a first right of refusal contract or something to that effect.