Is the tank ride thing in Mornington or on the Mornington Peninsula? The Mornington Peninsula is the whole region and Mornigton is a town in the middle of it. Sorry to sound like a downer but depending on where it is on the Peninsula it could still be an hours drive from Mornington IYKWIM.

You could hire a car for the day and while you're there drive to Sorrento for lunch or visit Arthurs Seat or one of the wineries etc.