Hey Bill,
Hope you're doing well.
The best thing I've found for copperheads (they require high humidity or they end up shedding like lizards) is cypress mulch.
Cypress trees are native to swamps, so the wood is built for a wet environment. There are natural mold-inhibitors in it. It can remain damp for long periods and doesn't mildew or mold. I love the stuff.
I would remove the snake when feeding though -- I had a mouse lay on a piece of mulch for a couple of hours. The snake didn't eat the mouse. I then took the mouse out of the enclosure, and low and behold, a copper ate a big piece of the mulch that smelled like mice.
He passed it fine, but it could easily have been an impaction. That could happen with most any substrate though. I've seen x-rays of a boid that swallowed a towel once.
Anyway, did you make it to the SC show? I was only there a couple of hours and headed to the state line to herp a mountain for timbers -- only found one garter though.
Chad Minter
http://www.envenomated.com