Hi, and congrats on getting a 2104S - we love ours. Bama Rambler is correct, the converter and panel is near the floor, under the oven and immediately to the left as you come in through the door.
Regarding weight distribution, we have 2@ 12V batteries in the factory tray on the A frame and our tongue weight is just where it should be. Seems like if you put them in the rear, you could end up on the too-light side for tongue weight but that of course will depend on what else you're loading, and where.
Jack & April Connell
2017 Rockwood Mini Lite 2104S
Tow Vehicle: 2014 Jeep Grand Cherokee diesel