I don't know the history of your particular unit but can tell you the breakdown of your serial number. The 18 is the length, the D is for the double bed and the 0233 is the number of your unit as it came off the assembly line or, in other words, the 233rd one made at that plant.
Congratulations!! Sounds like you've got a great unit. I love the little Travelers. Post pics when you can.
4CU 2699 / AIR 10 / TAC AZ-1
I'm haunted by aluminum.
Charter Member of the 4 Corners Unit.