I put my battery in the tongue box but I went with lithium ion because it is so much lighter. It’s definitely more expensive but it was a simple all in one unit so I didn’t have to worry about chargers or inverters.
There are some posts about mounting the box under the rear of the camper in a battery box. That might be the best compromise for a lead battery because it takes the weight off the tongue but doesn’t put the weight on the galley floor.
-mike