The solution if you are using a tank!

[scalrtn]

I've been having humidity issues in my 20 gal tank, so used this concept to make a similar top using foil tape - covered cardboard. I use a dual dome lamp with dimmers, which allows better control of ambient temperatures throughout the enclosure. Because the large hole isn't at the far end of the hot side, I made the air holes a little bigger...The humidity levels are now nominal at both ends of the tank. Comments/critiques welcome.

[Rickys_Reptiles]

I've been having humidity issues in my 20 gal tank, so used this concept to make a similar top using foil tape - covered cardboard. I use a dual dome lamp with dimmers, which allows better control of ambient temperatures throughout the enclosure. Because the large hole isn't at the far end of the hot side, I made the air holes a little bigger...The humidity levels are now nominal at both ends of the tank. Comments/critiques welcome.

Looks like a fantastic alternative!

[Reed12321]

I need to do this. I have a 20 gal tank and what I'm assuming is a 50 gal tank.