The flickering light basically is showing the direction current is flowing, either into or out of the chassis battery. A red light is outgoing, indicating the battery is losing charge. That would mean either a lack of incoming current (possibly a faulty alternator) or excessive outgoing current (e.g. multiple high amp devices running or charging badly discharged house batteries).
In terms of probability, I'd suspect either filed diodes in the alternator or a house battery with a bad cell sucking too many amps. You can have the alternator tested at many auto parts stores. House batteries can be load tested, but maybe easier to simply take them offline for a test drive and see if the lamp still flickers.
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