I briefly went through the same thought process, but on a new AF 990 (Sep 20th Del) and wondered about 6v vs 12v... and bigger 31s? as compared to the 29s.. (sorry, forget what they're called)
I was advised by dealer and it seems to make sense to me.
6v vs 12v -
- 6v I believe will have 'More Power longer" but that if one goes bad it drops to -0- power immediately until fixed.
- 12v as a little? less power duration, but if one goes bad, you're still good to go
Trays:
I thought about just going with the bigger batteries, 31 or ??? and they could do it but would have to take out the trays. The thought of trying to slide out to "Load/unload" a heavy batter up higher than my knees convinced me to keep the trays.. If need be, I'll get 1-2 more under the truck storage for additional batteries, but not seeing it as a "Must have" for now.
So for now, subject to changes an hour from now, heheh, I'll stick with the 2 @ 12v on the trays and go from there. Apparently the container bottom can handle the weight, but this is a new one, so?? dunno know on older ones..