I replaced the Univolt with the Xantrex unit for our 28 footer. We have only the two Group 27 batteries, so I felt the 40 amp unit would do.
If you're trying to run lots of 12 volt
stuff when plugged into shore power, the larger amp rating might be a better choice.
I've only used it twice since installing it, but it's quietly doing it job for us, and the batteries are 'floating' properly.
Got mine from Best Converter.