A T-234 Manufactured Home Certificate of Permanent Location sounds like what they must issue in your state when they retire the title? Most states have a system in place to reactivate a manufactured home title. Contact the department that issues the CPL and ask for a copy of the original title. It will tell you the year the home was built.
If you contact the home's builder they would be able to tell you the year and day the home was built.
Institute for Building Technology & Safety
is the national resource for information related to manufactured housing. They charge a fee to match the serial number with the rest of the information about the origin of your home.