In message ,
Muddymike writes

A jig saw with metal blade works well.

Cut about an inch below the lip and bell the bit left on the lid out a
bit. You then have a lid to stop rain getting in which will greatly
increase its life.

Had to read that a couple of times, but yes, that does make a great deal
of sense. The only thing that worries me slightly is that the top edge
of the drum will then be like a giant corned beef tin, so much care
required.
--
Graeme