Called Cruiser Overlander in Ohio and just Overlander in California, customizable with a 5% surcharge. 
Ohio had 4 flavors of 26' trailers this year:

Overlander, which was not customizable
"Monterey" (Experimental) (no nameplate, X-1005)
Custom layout trailers (O-8NNN-C s/n) w/ 10% surcharge
Empty shell ($2620)

During the year, the California plant changed over to the more familiar ramp shaped wheel-wells of the '57-'58 era.

During 1957 we also saw the change from 9 end-cap panels and the "whale-tail" to only 7 panel segments in California only, with Ohio lagging behind much later in the year as the form tooling was developed in California first.

This example is Ohio made O-7496.