I don't know anything about the LaPalma, but all the tanks on my Windsor are directly behind the wet bay where the sewage and water hookups are located. There is an access door on the passenger side of the coach that is held closed by straps and screws underneath.
The leak could also be coming from the gray or black holding tanks!
Good luck, happy trails, and God bless!
__________________
Joe & Annette
Sometimes I sits and thinks, sometimes I just sits.....
2002 Monaco Windsor 40PBT, 2013 Honda CRV AWD