All those things use chassis 12v power, so start hunting for chassis fuse panel and the chassis battery disconnect IF it has one. Could also be a faulty ignition switch (not engaging 12v power when key goes to On.
In a 1999, I would expect the leveler and step to be wired direct to the chassis battery with their own fuses, but maybe they are after the disconnect solenoid.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC