If you have no power to one ECM fuse, why would he think the ECM is bad? I would try to find out why there is NO power going to the ECM.
This could be a dirty connection, a broken wire, or a rodent chewed wiring harness. You have power to the ignition switch, other wise it would not crank. I believe coaches of that vintage seemed to have a problem with the ignition switch going bad and burning up internally because of so much power being drawn through it. Check all of the power going in to and out of the ignition switch as well as the connectors coming out of the steering column.