We are replacing the aft holding tank in our 1987 h40. Have a Lectra/San in the forward head. Aft tank was underneath the port clothes locker in the master stateroom. It held 13 gal. Looked at Ronco Plastics and it appears their model B495 10 gal tank is the only one they manufacture that would fit. Anyone replaced that tank in an h40? What did you use?