You have to pick a time you are happy to run the generator each day while camping. Then you can pick a charger and battery set-up that will meet that time.
You might not have the choice of times. Some state and provincial parks have limited "generator hours" so that sets the time. Outside of those times you must have an inverter to run any 120v items you want like microwave, toaster, kettle, TV/DVD, etc. You can do a 50-90 on two 6s in about two hours with a 70 amp charger.
So let's say you have two 6s, which can take about 80amps charging at 50% SOC, and you have a 2000w generator. It turns out you will need a power-factor corrected 75 amper or above to run on the 2000w (1600VA) gen, so that means a 60 amp non- PF or a 75 PF converter.
Everybody makes a 60 amp non- PF so wide open there. A 75 or above means a PowerMax. However the time it takes to do a "50-90", which is all you do while off grid (the 90-100 takes too long to dom on generator), is only 10 or 15 minutes longer using a 60 amper instead of an 80 amper on two 6s.