Hi michelle
I dun have those designed backgrounds from exoterra...i prefer the normal ones...makes my work easy though

Anyways...what i do with my newer setups is i just silicone the styro to the glass...and seal up all the holes i can find...
just so that theres no chances of bugs or frogs getting lost inside.
Not so big a problem as when u want to change your design later, u can just slice it off with a sharp blade...

Well for me that's not a big problem though...