I had the same problem with my Xantrex Freedom 458 2000; high voltage on a cheapie meter verified by my Fluke True RMS. Since my coach had indications of voltage issues before I purchased it, I wasn't surprised. Fortunately, my "stuff" is stored in Portland, OR -- one of the few locations of a Xantrex authorized repair center, so on a pass thru to fondle the stuff in storage, I dropped it off last fall.
DC board was defective, tech advised replacing the AC board as well since it has a history of failure. The repair was roughly half that of new, the magic threshold, but it's still a current model; so opted for repair since it's not in regular use. Unit was only in the shop overnight. I'd question whether a non-authorized shop would be efficient enough to avoid racking up labor charges -- I paid the minimum.
Not sure this helps, but I'd recommend finding an authorized repair center -- I feel it paid off for me. Surge protector is not an issue in your case, voltage regulator would be. Calling Xantrex will probably be marginal help. Call a repair center.
