In Missouri you can use a license plate from the year your motorhome was manufactured. There are some restrictions, but from what I have seen, they aren't enforced much.
I've copied what is listed from the state:
A vehicle that is registered as a historic vehicle may be driven:
To and from exhibitions and educational events without any mileage limitation;
To repair facilities within a 100 mile limit; and
Up to 1,000 miles per year for personal use.
Year of Manufacture License Plates
The owner of any historic vehicle possessing a license plate issued by the state of Missouri that is over 25 years old in which the year of issuance of such plate is consistent with the model year of the vehicle may register such plate as a Year of Manufacture historic vehicle license plate as set forth in section 301.131, RSMo, provided the plate configuration does not conflict with the current numbering system. If you already have an old Missouri license plate (or set), you may e-mail the plate configuration to firstname.lastname@example.org
and ask our staff to verify if it is available as a Year of Manufacture registration.
To apply for Year of Manufacture license plates, you must submit the following items to our central office in Jefferson City:
A completed Application for Missouri Historic or Personalized Historic License Plates (Form 570);
A picture of the license plate you wish to use for the Year of Manufacture registration;
A paid personal property tax receipt (original or copy) or a statement of non-assessment from your county of residence (or city of St. Louis) for the previous year;
A current insurance identification card (original or copy) or other proof of financial responsibility;
A copy of the vehicle's title or registration receipt;
A registration fee of $25.25 (this is a one-time fee);
A $3.50 processing fee.
Be sure to mark the "Year of Manufacture" box on the Form 570.
When selling a historic vehicle with a Year of Manufacture registration, the new owner may use the Year of Manufacture license plate(s) on the vehicle if the previous owner provides a relinquishment letter, and standard Year of Manufacture requirements (above) are met. There is no limit to the number of times the plate may be re-used as long as a notarized relinquishment letter is provided.
If you have additional questions about historic vehicle registration, you may send an e-mail to email@example.com