Good day John!
Because of the Petter diesel it sounds like your boat is of the same vintage as mine, so perhaps my boat's set up will help you.
I currently have a Tempo 11 gallon tank that lives in the port-side cockpit locker. This tank is a replacement and I recently discovered was poorly fitted -- instead of resting on its plywood base it sits on one of its corners pressed hard against the hull of the boat -- a situation that is neither good for the boat nor for the tank.
Based on the dimensions, I believe that the original tank on my boat was a similarly sized tank by Vetus. Its rounded corners would have made it a much better fit. Unfortunately Vetus tanks carry a Vetus price tag which is probably why the Tempo was used as the substitute.
The good news is that I bought a 5.5 gallon Vetus tank on E-Bay over the winter. Since I am lucky if my boat consumes more than a gallon a season, this will be sufficient for my purposes and if I can mount it in the main engine compartment then I free up a cockpit locker to boot!
Perhaps my old Tempo tank would be of interest to you? Unfortunately shipping a smelly fuel tank will be a problem so unless you are close to Montreal...
Cheers!
Christopher