Are asking if you can change the 30 amp breaker in your RV to a 50 amp? Or if you can change the 30 amp breaker at your house to a 50 amp?
If your RV has a 30 amp breaker in it, then changing the house breaker to 50 amp will do nothing for you. You are limited to 30 amps by the RV breaker. And you do not want to change the RV breaker to 50 amps.
As stated above, you need larger wire for that 300’ run. Have you checked your voltage level in the RV? Probably dropping too low with those things running at the same time.