In the Transit build I'm working on, the generator feeds a Magnum Energy MSH4024RE inverter/converter that takes two 120VAC sources as well as batteries. It is $2319.20 on Amazon, and $2245.00 at Wholesale Solar, but it makes things like damaging voltage sags a thing of the past. Plus, it can be connected to a generator controller so it can automatically start a generator if the batteries hit a low water SoC mark, and stop the generator when the batteries hit a high water SoC level.
The inverter isn't cheap, but it does allow for a generator to be a tad off with regards to voltage or frequency, and not affect anything else.
