Dual batteries in an older Lance?

On my old Lance 1080 which only had room for one battery. I put another in front of the wheel well in a battery box accessed thru the little doors into the wheel wells from the inside of the camper. I made up heavy cables & drilled the plywood floor behind the lance battery holder (in the sink area) & ran the cables "down" to the new battery box. This area was ventilated well enough I believe & never had any problems. One did have to be careful hooking up the cables though & remember to remove the box & battery before taking off the camper.
Of course I had tight holes & sealed around the cables thru the holes drilled. Never smelled any gasses, (at least from the batteries that is) ha ha ha!