RE: New camper without 12 volt fridge
The newer one have a 12 volt compressor fridge which are very good and do not use the same power as the old units that heated up and drew lots of power and killed battery. Add a solar panel or two and you are good to go.
RE: Slide Electrical Issues
Low battery voltage. If it works when plugged in the converter is putting out 12 volts to operate your motor. Check wire to battery and clean if bad.