Building the quick and dirty Churchill, I found some pictures of Churchill tanks carrying these helmets on the stowage areas.
I wanted to have that detail but I didn’t had any British figure set laying around so this is what I came up with.
You will need a circle drafting template, some lead foil (I take mine from wine bottle covers… hey it is a hard work but somebody has to do it!) and the round back of a paint brush, or similar tool.
Select the 3mm circle, put the foil on top of it.
Gently press the circle area with your brush, if the lead foil is thick you can try spinning the brush.
A dent on the foil should be present now, if you got cracks in it, or if it is pierced it is OK. Just try again with a bit less effort.
Once you got your shaped right, cut a circle, 1mm around the dome you just pressed into the foil.
Presto!, for durability you can fill the inside of the helmets with cyano glue. That way they will not change shape when handling… or you can directly glue it to the model.