The Hardway is to uninstall a lot of parts including the seats and carpet to meisure by myself
You might be able to slip a tape measure in the access hole(s) to get the dimensions. Some below deck tanks are "V" shaped on the bottom.
Are you wanting to replace it?
the fuel tank is Plastic and can hold up to 35 gallons,
But the problem is that he likes to chunk the gas over the fuel sender, there is no matter If I change the gasket, there is anyway to avoid this???