I'm not sure I can help but since no one else has answered, I'll try.
First, do you have the converter and inverter correctly identified? An inverter takes 12 vdc and outputs 120 vac to run 120 v items when not connected to the grid. The converter takes 120 vac and outputs 12-15 vdc to charge the batteries and run the 12v things in the RV. Inverters usually have a switch, converters usually don't. That vintage Magnetek converter probably outputs 13.8v.
If you have the converter correctly identified, and there is nothing wrong with it, it will charge the battery. You might want to measure the output voltage.
The Magnetek converter is not a good converter by todays standards. You may want to update to a modern converter. You will get faster charging and longer battery life.
Class C, 2004/5 Four Winds Dutchman Express 28A, Chevy chassis
2010 Subaru Impreza Sedan
Camped in 45 states, 7 Provinces and 1 Territory