Preparations for Waterloo 200

At Waterloo in June 2015 I will be portraying a major of the 1st Foot (Royal Scots).

I have been working on the bicorne hat which I purchased on Ebay, and have achieved this:

A British staff officer's bicorne of 1815.
A British staff officer’s bicorne of 1815.

But apart from the Waterloo event in 2005 when temperatures reached 38c (100f), every reenactment I have done in Belgium has been wet and muddy, so I have made a cover to protect the glorious appearance of the headgear.

Suitable for Belgium?
Suitable for Belgium?

I searched the internet and every reference book I own for a pattern for the waterproof cover to no avail, so finally had to design my own. I find it amazing that although there are so many references to covers for headgear in this period there is little evidence as to how they were constructed.