I was in a Christmas shop yesterday and saw some pan scourers in white. It is about 5mm deep and perfect for broadside markers as it is easy to cut with scissors to any shape required. If you wanted it would be possible to paint the side pressed against the boat with a bit of black or red to show the layers of smoke and powder shot out of the guns.
I think my eyesight is gone enough that I would not be able to tell the figs had the wrong pattern of lace on the turnbacks or the wrong number of buttons so the figs could be used over a wider period than intended,
