Last year for the 16' Bubble.  Another 16 foot trailer won't come along again until the 1960 Pacer.  For 1957 the California Dutchman 9 panel rear end is gone, replaced by front and aft 7 end cap configuration.

Only one Ohio trailer appears to have been made in 1957, and only one other the following model model year (1958).

The canvas canopies were a popular option, and attached to a rail on the trailer, supported by poles and guy ropes. Serial # 437 shown here also has full matching side wall panels.