The dual battery system consists of a larger starting battery (100 Ah) in the default location and a second battery (110 Ah AGM) in the right rear corner.
The Hella Supertone horn kit is almost a direct drop-in replacement for the stock horns. I would estimate these horns are about 30% louder than stock.
I’m installing a kitchen under the bed. A Waeco/Dometic Coolmatic CD30 drawer fridge is perfect for this.