I researched what I could find, and based on Genesis having made radios for certain cars, and what antennas were available for those cars on ebay, I took a chance on this:
JDM REAL CARBON FIBER FM/AM RADIO 6" LONG RANGE ANTENNA SCREW TYPE
It comes with adapters, but they were not needed, as the antenna base has a female M6 base thread, and screwed right on to the original camper antenna base. I used the enclosed plastic washer to ensure a snug connection.
AM is fair, and FM is good, so I am happy with it. $10 and delivered with fast shipping.
Also, it looks good.