Sorry for sounding dumb, but here goes. Is it necessary to have one of those water wiggler things to put the temperature probe in? I built my incubator out of an old cooler using gopher boys design. I have the same thermometer hygrometer that he used. I am not sure the right place to set the thermometer and probe. right now it is taped to the egg tray between the eggs and the probe is laying on the opposite side of the tray. The temp readings are rarely the same, with a bigger difference when the tray is turned toward the light bulb. Yes, the light bulb is shielded. The temp vary by as much as 3 degrees. What am I doing wrong?