I'm using Schedule 40. I found a local chain that has thinner walled pipe that might work as a sheath if I don't go past the emitter, but it's much more expensive. I've also cut a sink pipe as a sheath that worked out pretty well when mounted over the PVC pipe. The only issue I have had with the schedule 40 is fitting a battery pack. I can't use the AAA packs that Tim offers so I create a sled and mount two double AAA packs nose to tail and they fit perfectly. The two packs will need to be wired in series, but it works really well.

Needless to say, i have a few extra 4 cell AAA packs kicking around.

Jon