2002 Newmar Kountry Star reoccurring electrical problem

For testing purposes, plug in using a 30 amp to 50 amp adapter. That puts voltage on both legs, but it is the same phase so there is zero voltage between the two hot wires.

Now, you can look for wherever there is no current/reduced current/low voltage without risking damage to anything plugged in from 240v. A loose neutral under those conditions will just look like an open circuit or loose connection.