You are correct that on a 50 amp service you can have one side of the feed a lower voltage since the 50 amp is actually two separate 110 volt feeds.
I have seen on our Progressive EMS where the voltage on one feed can be 5 volts or more lower than the other leg.
That is one of the reasons we purchased and installed the Progressive EMS. It monitors the voltage, amps, and many other things. NO I am not associated with them, but just a happy customer.
The unit costs appox $300 for either the potable unit or the hardwired unit.
You can check them out here: Progressive EMS
I purchased the PT50, then I cut the cord on the coach and installed a plug so that I can keep the unit in the compartment at all times. It helps to keep it that way!
Also, If when purchase a different coach we can take it with us.