50amp wiring question

If you really want to live off of 30 amps to save money my guess is that you want to do it for as little cost as possible.  This basically means that you need to avoid running more than 2 major power draws.  And, you probably don't want to run your water heater on propane.  Probably not you stove either.  Propane is expensive and not included in the cost of your campsite.

So you get to chose two things to run at any given time.  Once your batteries are charged up your shouldn't need to worry about you power converter as it will just be supplying whatever is currently running.  Hopefully you have LED lights for a minimal load.  An RV refrigerator  on AC power generally runs about 2 amps max if you don't have or use an icemaker.  So, run the AC and carefully choose when to run the other electric devices: water heater, microwave oven, electric cooktop, hair dryer, etc. and you should be good.  

One major concern left, the two AC units on my 32ft motor home struggle to keep it cool in 95 degree heat and it is fairly well insulated.  Electric cooktops put a lot less heat in the camper than propane and induction cooktops put in less than the resistance type.  I have a double burner type.  It manages the power load to help prevent overloading the circuits.