We faced the same issue you did. I want to make sure we have 220/50 at all times because while I'm very careful and am very unlikely to accidentally run the washing machine/dishwasher/microwave on 60hz shore power, I can't rely on new crew always remembering.
Here's my system, as you may know: Victron Quattro 5000w/24v/120amp charger/inverter, 450AH lithium, Victron Skylla-i 80amp second charger.
Right now, if I find myself with 250v/60hz power, I will plug in, if necessary, to charge the lithiums and then completely unplug. This rarely takes more than 2 hours. My current system is wired so shore power goes to the Quattro first (which replaces the Amel transfer switch, too) and while it charges using the 120amp Quattro charger, it will also passthrough the 60hz power to the boat. That is obviously not ideal. I have confirmed with Victron that there is no way to disable this passthrough when shorepower is detected.
My Skylla-i is wired on the second AC output on the Quattro to avoid running the Skylla charger when the Quattro is acting as an inverter. I did this because 99.99% of the time I'm not in a marina, so I would like to be able to charge using both the Quattro and Skylla (200 amps total) while on genset.
This works great for me as we can run everything on the inverter/batteries. The aft AC will easily run all night on battery. If it's 40c and we need to run multiple AC units, that might be different.
A possible improvement would be to wire a switch somehow so that it's wired as a described above normally but you can flip the switch and have the 60hz shorepower only go to the Skylla when plugged into 60hz shorepower. That way, the skylla feeds 80amps DC to the batteries and the Quattro, not seeing shorepower, would act as an inverter and supply 230/50hz to the boat.
Note that the Skylla-i will take 60hz, but it must be above 185v. I'm sure you could find a "world capable" 100-250v/50-60hz charger, but we couldn't find one that had high output and was compatible with the BMS, which is absolutely necessary when charging lithiums.
If you don't want to add the second charger and you have a solar MPPT and you won't find yourselves with the 60hz problem often, you could simply get a DC power supply and feed the DC output into your solar MPPT. A 30amp DC power supply can be had for less than $100. Not ideal but works well enough for occasional use. It's also a lot simpler and cheaper.
2007 A54 #69