I want to install a holding tank under the starboard V-berth. There is a small one there now. The opening is about 19X15" The space is about 30" long and wider in the back. The space below the opening is about 4" wider than the opening. Inboard it's about 25" deep and 10" out it's about 19" deep. I've found a tank that is 16X12X24. Short of making a model is there any way to see if it will fit?? I don't want to remove the old tank until I'm ready to replace it with a new tank. I plan a standard type of installation with everything going into the tank and a Y valve to a deck pumpout or a hand pump overboard. I plan to use 1/2" plywood as a platform and then strap the tank in place. Thanks