JulieZ - The wire mesh goes on the Water tray.first put the sponge in the tray.the sponge will help along with humidity.
Then wire the tray with the mesh and tape along the ends with duct tape so that the fan doesnt fall into the water tray.
The sheet of glass goes on top.you will get good humidity.You will also see that the sheet of glass doesnt cover the whole lid because of the fan cord.this doesn't matter much.If you dont get your 75%humidity,then slightly cover the gap with duct tape until desired humidity.Do not put mesh on the top of the aquarium.the glass goes on top.
Here is the top view.Notice the glass on top:
Here is the gap from the cord of the fan.here you can put duct tape to fine tune the humidity.:
Here is a close-up of the water tray w/fan on top:
Assembly of water tray goes like this:
first get tray,put sponge in tray then mesh on top and around sides.you have to cut the corners of the mesh to make a sufficient lid.then get duct tape and tape around the tray on the mesh to hold the mesh down.insert tray into incubator,add water into tray.Place fan on top of tray.