Part of the answer depends on whether the mobile home has been affixed to your property or is located on a rented lot (such as in a mobile home park). If the mobile home is in a mobile home park then you would need to transfer title through the department of licensing (see link below). A sales contract in this case would not be recorded.
If the mobile home is affixed to land and the contract is for sale of the home and the land then the home would be sold through a real estate contract like other homes and real property. There are documents that should be recorded, such as a deed or deed of trust. A sales contract is also often recorded if the sale is seller financed (i.e., the buyer makes payments over time to the seller in lieu of a lump sum payment for the price of the residence). You record such documents with the county (usually the county auditor) where the property is located.
Real estate transactions can be complicated so its advisable to use an attorney, real estate agent, or title company to make sure you have all the required documents.
Providing this general response does not create an attorney client relationship.