Want a "bigger" battery but where to put it?

First I would try put a genuine Concorde Lifeline AGM group 24 battery and see how it does. If it lacks reserve capacity then you can start thinking about sticking a similar brand group 31 inside the rig. Bit by bit without wasting a nickel.of your investment.

There are cheaper brands of AGM batteries out there than the Lifeline. But then there is the Yugo as compared to a Toyota or Rolls Royce. Your converter float voltage will work fine with the AGM then connect only a battery tender for long storage periods.