I don't know what converter you have but I suspect it's most of your problem. The factory converter in 2003 camper will only put out 10 amps to the battery. It's rated for 45 amps I think supplying lights, pump, etc. but only 10 charging the battery. I don't understand that design but it is what it is. If I camped more often without electric I would upgrade but I don't do that enough to justify and I have 100 watts of solar anyway.
You're converter, being even older, is likely no better. A good aftermarket stand alone battery charger would probably help things considerably. Or, upgrade your converter.
