Without the battery, all 12 volt items should "work," however you run the risk of damaging the converter if you try running a high demand item.
The camper's electrical system is designed to work off the battery and converter to just keep it charged.
It would be like driving your car without a battery and using a battery charger to start your car.
Bad for the alternator.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW