While a COP would certainly be good, I personally think it would look great with a simple globose breastplate. Nothing fancy, just a single formed piece of steel with no rivets or articulations, like this one:
(img)
http://www.james-anderson-iii.com/_content/thearmory/pages/europeanarmor/large/128.jpg
That looks familiar.
It's stainless, but has a black finish. The black is flaking off all over my floor, so I'm assuming it'll wear down and be less black over time.
Mine is doing the same, and oily while doing it, too. I've read about throwing it inside a few pillow cases and putting it in the dryer, but I think I'll take the safe route and get some sand, throw the mail and sand in a bucket, secure the lid on the bucket and roll it around for a while.
I saw a *really* nice setup drawn up many years back. It was a scale "skateboard" half-pipe that had a cutout directly down the middle all the way through, and a barrel with a ridge all the way around it that fit into that cutout (same concept as a train track). It was maybe 5' long and 4' high, as a best guess, ideal height would probably depend on the weight of the mail and how high one can lift it easily.
You would put the mail and sand in the barrel, secure the top, then lift it up the halfpipe and place it in the notch, then push it over the edge. It would roll down the halfpipe and up the other side, and would keep doing so for 4-6 times, so that you didn't have to constantly push it around.
It was designed to remove rust, and is based on (what I understand to be) period references to barrels of sand and other abrasives that were used to clean and polish the mail. A better alternative is a squire of course, but lacking that, it's a cool idea. Never did see one actually constructed, though the concept seems sound.