We took a 30 day "out west" trip in 2010.
Over half the time we were on shore power at various campgrounds but
we had several road trips some all day long and some dry camping.
I was surprised to use nearly 2 full 20 Lb tanks in that time.
I can't say how much we heated water.
Not a lot, some days we just pile the dishes.
Some days we'd turn on the WH and wash them.
Like I said, I was surprised to use that much.
I'm with Chap on this-- why do you think you need Two 2KW gennys to
FYI, A 25 AMP 12v battery charger only draws about 300-400 watts of 120 v ac.
Now if you're planning to run your roof air, you probably need dual gennys
but for charging batteries One 2kw is overkill.