MY PERSONAL OPINION:
ok, you asked about the solid background. If you can find the right material I think it is just fine. It shouldn't cause any ventilation problems. You just need something that won't rot or be toxic or cause problems of any sort. Do you already know what material you have in mind?
The partition in the middle (still, just my opinion) needs to be more than just screen. If they can see eachother, they will stress eachother out. I have dark dark shade cloth that separates my chameleons that you can't see through. I have it double layered. That works for me.
I would also think that this enclosure is too large for little chameleons. You will want to see them. It will be hard if it is this size. Also, little chams might not be able to find the food. I suppose you could put LOTS of food in the cage, but that can cause problems. Anyhow, these are all just my opinions. Take in what everyone says, maybe no one will agree with me.
Chris Fullmer