I think this is the most likely scenario for a burned up cord with no (or late) breaker trip.
Corrosion at the wall socket of the camper.
A corroded, pitted connection can increase resistance (and thus current demand) at the socket that the 30 amp breaker inside the coach does not "see" (so it will not trip and end the high resistance short at the socket).
Temperature at the bad connection will increase at the wires until something gives (the wires, the socket, or the 50 amp breaker).
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW