Two 6 volts or Two 12V series 27

[LI Pets]

I'm redesigning the front end into a wrap around dinette.

First question is I want to place them about 2 feet aft of their current position to reduce tongue load.

So space is not a concern, I'll use the battery box door to access parts for propane, hitch, jack stand blocks etc.

I'll also replace the univolt with something more up to date.

So what batteries are the best bet considering cost, weight and amps