You can run it on either propane or electric if your camper is 1) level and 2) plugged in...3) you have propane to burn (duh
) It's up to you which to use... It makes sense if you are 'plugged in' that you would want to use electricity... this is what the 'Auto' switch on the norcold is for. It will switch to electric if available, and if not, it will run off propane automatically. If your electric is coming in from a generator, that works fine. The fridge doesn't care where the power is coming from.
The bigger issue is 'hubby doesn't want to charge it with the generator'... This is kind of a moot point because unless you level your RV, you shouldn't be running the fridge at all.
If you don't have shore power (or a running generator) running into the camper - you have to use propane. You want your camper to be level regardless. Both propane and electric operation require this.
The only time you should run your fridge when your camper is not 'level' is when you are on the road, driving as this keeps things sloshing around enough to prevent any problems with the fridge. If you can't park on the street to 'pre pack', you'll probably have to get by with putting your fridge items in at the last minute, turn it on, and hit the road.