Hi,
My "break out box" for 50 amp to one thirty and two twenty amp plugs has individual breakers for each circuit.
50 amp plug-->box-->leg #1-->30 amp breaker-->30 amp female outlet.
=============\->leg #2-->20 amp breaker-->20 amp female outlet.
===================\-->20 amp breaker-->20 amp female outlet.
Inside the RV power panel as it happens my converter uses a standard 120 volt plug. I simply added a cord (20 amp) with one outlet by the power center, and two extra outlets in the bedroom area.
For the water heater, I chose to to use 15 amps with again an outlet close to the power center, and one additional outlet.
When I'm at a home that allows me to use up to 3 15 amp circuits giving me pretty much full functionality on the Rv.
At a campground with 50 amp service I have the OEM 30, the 20 secondary, and the 15 amp tertiary if need be. If there is only 30 amp I can quickly change back to the OEM configuration. Sometimes there is a 30 and a 15 at the campground. When that occurs I plug in the water heater to the 15 amp--and then I no longer have to worry about power management.
One added side benefit is that I have run up to 6500 watts of electric heat in the winter, and not pay extra.