Is it ok to block back wall with cork bark?

Hi, I'm getting two slings next week, .75" avicularia geroldi and ybyrapora sooretama. So I'm planning out their first enclosures, first arboreal setups for me.

I know ventilation is paramount, so I got 3x3x6s with ventilation on the top and 3 sides. But I want to ensure climbing safety at the same time and plan to put cork bark along the back side.

Is it OK to block the back ventilation? There will still be cross ventilation and all of my guys are beside an air purifier to give them a bit of a breeze and prevent stagnant air.

Is this a good plan or should I reconsider?