Second, WHO SIGNED THE CONTRACT FOR SELLER? If you don't have a signature, by the lawful seller, you don't have a contact, I would think this maybe the case as it sounds like the manager delivered the contract to the seller. DOES this manager have a Real Estate license (FS 475) See
or mobile home (FS723) See
If the mobile home manager was authorized to sell, to sign contact, under 723, then you may own a $50,000 mobile - see a Lawyer.
If he signed contract and was not authorized to do so, then you have other possible options against the manager and maybe the park, as well as possible actions by the state. See a lawyer.
If this involved land as well as the trailer, then everything changes - See a Lawyer.
Did I mention you need to see a Lawyer?