If you are taking the genny as backup, it may not matter so long as you are comfortable with running it for hours a day.
If you want to try more boondocking I would go with the pair of GC-2's. More usable amp hours than a pair of group 24 rv/marine batteries (almost double) and you can expect a longer life since you wont be running them as hard compared to their ability.
You may find that you wont be using the genny any more than every other or every third day with the added battery capability.