Polyrama Plastics that made the tanks for the boler
has been sold to Norwesco and do not list the tank anymore. Better contact them to see if its still available. It does fit the Ventura
but requires the cutting of a new hole in the floor to run the fill hose as the Ventura went through the top of the tank and the new one has a side fitting. This will require a bit of fiberglassing to patch the old hole.
I got mine 2 years ago and they were about $100 and they said they sold about 10 a month