Propane tanks are not all standard dimensions... best to take a tape measure to your locker, then take the measurements to where ever you plan to buy the tank.
The newer fiberglass tanks are great, no rust and you can check the level easily. They are in some ways bulkier than the older tanks.
Unfortunately the smaller more compact tanks seem to be getting harder to find and disporportionately expensive.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)