If your chassis batteries are draining while in storage, it won't likely have anything to do with parasitic draw from anything in the coach. Instead, it's something in the chassis circuit, and could well be the radio. If you really want to find out, disconnect your chassis batteries from the circuit on the positive side. String a test light between the cable and the positive battery post you removed it from. The light will illuminate. Start pulling fuses, beginning with the radio fuse, until the light goes out. That's likely your problem. If the light stays on after disconnecting the radio fuse, then you have more than one draw, any one of which could be the culprit. First, make sure your batteries are not only above 12.5 volts when disconnected, but have them load tested.