[Chris S]

I just use egg crate to fill in the blank spaces, and silicone the mesh onto the egg crate. Makes it more sturdy in my opinion. The edges of the mesh can be siliconed to the glass and top frame of the exo-terra.

 

[Chris S]

Went through and cut the egg crate apart using some cheap wire cutters that I'd purchased for a different project. While it's cleaner than scissors, it's still fairly pointy. C'est la vie.
The entire thing is 3 inches wide while the open area is 2 inches wide. That's at least a surface area of 113cm^2. Should be ample ventilation. I'm also currently running a fan over my vivarium to help with airflow so it should hopefully be fine.

One final question, how do you go about attaching the screen mesh to the egg crate if there are frogs currently in the tank.

Probably won't work.

Do you think the small eggcrate beams are enough of a contact point between the mesh and the silicone? Or should I silicone some poster board over the egg crate first and then silicone the mesh to that posterboard?

The above isn't quite what I do, but may work. Mesh can be siliconed directly to the eggcrate and directly to the plastic frame of the vivarium.

If you are worried about pokey bits, put screen on both sides of the egg crate. If there are any parts that are really pokey, plop a bit of silicone over them and they will disappear!

To make sure there are no gaps, I always put the screen on the (flat) bottom part of the egg crate, and then silicone it flat to the front edge of the plastic rim and on the bottom of the glass. That way there are no gaps.

 

[Chris S]

If possible, try to remove the frogs for a few days in a temp bin, then do it properly!