When it comes to building a permanent, secure top for the tank, keep in mind that you will need to be able to have access to both sides of the tank. If you have only one door, then it will be difficult to get into the opposite side.
I have a 55 gal with a top that is mostly screen, but has a round lid on either side, so I can just unscrew it and get in from there. The sides of the top have hooks, so I have attached bungee cords to keep my girl from escaping.
As a non-permanent solution for holding the heat and humidity, I just use plastic wrap under the screen-top to cover about 80% of the tank. It works for a quick fix, but is kind of a pain in the butt. That's why I'm ordering from
www.boaphileplastics.com very soon!
