Unless modified, for a Damon RV, the dash radio is powered by the house batteries, so you can enjoy music while camping without fear of killing the engine start battery.
So, forget the engine and alternator for the radio.
The house batteries must be connected (salesman switch near the entry door set to on/use) and the batteries charged to run the radio...unless you are on generator/shore power.
As described...The radio would be getting juice on the generator by the power going through the 110V to 12VDC converter/charger (battery bank connected or not).
Safe travels