That number was a WBCCI membership number of one of the past owners of the trailer. If there is a star or stars next to the number that indicates each 5 years of membership for that individual.
Membership does not go with the trailer but you could call the WBCCI headquarters in Jackson Center OH and see if the membership has lapsed and request it if you intend to join the club. No other reason than nostalgia.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles