I use a 40w appliance bulb also. I do have trouble with my water sliding off the cookie tin. don't know if roosters are chasing around it or what the problem is. Working on a solution for that, but kept water thawed inside coop no other heat in there.I have a plastic waterer on the cookie tin. I also have a heated plastic waterer that works well.
I had the same problem with my cookie pan heater. My chickens would try to jump up on top of the waterer, and the waterer would just slide off the cookie tin. I found a simple fix for mine. I just hung a small chain from the ceiling, with a cheap snap hook. The waterer is not really suspended by the chain, but the chain is in the way and the chickens don't try to jump up on the waterer. Works for me. Good luck. (Want to see it, Check out the interior pics in the Woods House in winter thread.)