The number identifies the owner of the trailer to other members of the Wally Byam Caravan Club International to each other. The number is held by the individual, not the trailer and is supposed to be removed when the trailer is sold or traded in. I have no clue on the movie info. If the number is available at WBCCI Headquarters you could ask to have it assigned to you and then people in the club would know who you are and where you are from when they see you in a campground or going the other way down the road.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato