How to track down water leak in NL camper

I have a book that says water fill tubing plumbed down to the tank is corrugated hose and needs to be caulked inside the hose or nipple at the water fill fitting on the camper body or it leaks when filling tank w/ freshwater. I had to do mine by cutting an access door in the top of the battery box with a razor knife, I could then get to the screw clamp and take off the corrugated hose and caulk around the nipple and slide the corrugated hose back on and reclamp. I then taped up the fist size access door inside the battery box.

Mine was leaking out the jack mount bracket each time I filled up with water and this book set me on the right direction.