the photo by dbir is typical. Two pieces of angle iron form a bottom and sides that the battery
box sits in, the strap holds the box in place and the lid on the box. Some have the box bolted to the angle iron. I prefer strapped because I remove the whole battery
box for storage in the garage.
You want about 10% of your trailer weight
on the hitch, putting the heavy battery
on the tongue helps in getting that desired weight
distribution. Often water tanks and rear storage inside and outside on bumper can leave the camper tail heavy, which makes them prone to getting sway. Propane
and battery put heavy in a good location.
Blasted things are heavy! I don't want to fiddle with trying to lower them into some under seat or slide them into cabinet storage. Drop that puppy on the tongue, connect it, strap it and done. If I do drop the battery outsdie.... hopefully it misses my foot. But it won't be smashing up the camper or spilling acid on stuff.
For a portable solar
rig as others have mentioned it seems like it would be easier to hook up. My Scamp
did not have one, or a place for one. As built it got power only from the TV.
There are batteries that are supposed to allow for inside installation, more money.