[RDVAARK]

I also was faced with this absolutely awful, horrible, dilemma. I looked around for something more aesthetically pleasing and found a 2" dia flat medication can with a slip off cap. When closed, the cap holds the can on the engine side in only as far as the raised lip (sort of like an old Esquire shoe polish can). An added benefit is the conversation that ensues after the curious fondle and examine the can to read the label which states that it is to be applied to sheep with a urinary infection. It IS period correct, and is a somewhat attractive light olive green with black lettering and a silhouette of a sheep on the label. The engine side is rather plain. In the future I plan to fill the empty can with suitable insulation to exclude engine heat from the cabin. I may also coat the inside of the can with brush-applied Glyptal, so it doesn't corrode at elevated temperatures. Really.

This only works on flat areas of the 28-29 firewall.