When we bought our boat
, there was an old Xantrex RV3012 charger/inverter installed. It was working and I saw no reason to replace it. I did install a Charles Marine
transformer to drop the voltage to 120 Volts.
When we were preparing for our trip across the Atlantic, I had the same questions that you do and I contacted Xantrex about the AC frequency specs for the input. I got a very short response which, in it's entirety, read "Dear Steve Brown, It's best to use 60 hz. Having a 50 hertz frequency could damage components if there not rated for that frequency. Best Regards".
I ignored that advice and figured I would try it myself and replace the unit if it failed. Result - we have been here in the Med since June, 2015 and have been plugged into 50 Hz shore power
close to 2/3 of that time. I have had no problems with the unit working with a 120 Volt 50 Hz input. It still works perfectly.
Just my experience with my old Xantrex. Cheers and best of luck!