No experience but google search found this:
These are paragraphs that apply;
NOTE THE EXCEPTION
One Vehicle Per Eligible Person
Only one vehicle can be imported into Mexico per person. If you are traveling with your spouse or child over 18, they may each register one car in their name.
There is one exception to the one-person, one-car rule: if you tow a car behind your RV, there is no need for second person to be traveling with you; but you must show proof of ownership for both vehicles, and both vehicles must be taken out of the country together when you leave.
Motorcycles, ATVs, etc.
If you are towing or carrying other single-passenger motorized vehicles these may be registered with the car that is towing or carrying them. You must show proof of ownership of all vehicles and you can only bring up-to three single-passenger vehicles--one each for up to three passengers traveling in the main vehicle. All vehicles must be exported together when you leave Mexico.
Like most "Offical" crap I'm still confused but the Exception says you should be able to haul in your moto.
Make sure you have "Origional" registration, not a copy.
I almost did not get in with my copy ( I assured her it was an "Origional Copy" and she said OK this one time only) Whew !
Spent a week there last March after reading Triceplolts Ride Report (check it out in his signature line).