The 12a charger is fine on the truck. Charge monthly for 48 hours assuming it shuts off automatic. Or at least the night before you need it. Batteries might be getting weak.
Often when charging by generator we shoot for 90% because that is fast 2 to 4 hours. The last 10% just takes another 6 to 10+ hours depending on voltage. To minimize generator time the last 10% is ignored until utility power is available.
AFAIK the 6332 does not have a float. It actually has two power supplies. One for operating the RV (32 amps)and a second to charge the battery (6 amps). Voltage tends to run high on these so they use more water in hot weather. Changing to a three stage charger was not a waste as you will reduce battery maintenance, extend the battery life and have a more versatile RV.
As a shop charger it will be weak. Although I believe you can adjust the voltage manually. The power is fairly rippled and generally needs a battery as a filter if using as a power supply. I would ebay or pitch it.