IN my coach I found junction boxes behind false wall panels, behind cabinet drawers, and under the sink in a slideout. The manufacturers have many places they can hide junction boxes. Also you might not want to discount the fact that a rodent could have chewed a wire somewhere in the rig.
In any case, have the guy disconnect ONE outlet at a time until he locates the "area" where the short is located. This should help him locate the problem.
If one outlet feeds to other outlets, there will be two black wires. Only one black wire means you are at the end of the run.