Generators are not good at maintaining/floating batteries, they are more suitable for running 110V loads or charging batteries. Preferably, charging ~100% each time - which job generators are not good at either, may take many hours. If you can't do 100% most of the time, you'll have to equalize them once a month or so, unless you are prepared to throw them out in a year or two.
1000W is enough for 2*100AH batteries, provided you have an adequate converter or charger. OEM converters in most trailers are cr-ap.