M_Boats: Need help with a porta-potti

Kendall Docter M-15 #164 I'm looking for a used Porta-Potti for the M-15. I remember reading somewhere that Jerry was surprised when Porta-Potti changed the dimensions. He suggested that guy put really hot water in the Potty and force-mold it into the hole, which apparently worked. The dimensions I was given don't come that close to me seeing that trick work. There is a used one on Bay and I'd like to bid on it, but the measurements are too big, and it is the right model number. Maybe the woman didn't measure correctly. Any suggestions?