Well I ordered some food-grade silicone regardless, based on our conversation last night. IIRC, the conversation about kitty litter partially revolved around not knowing if I would have an electric box. Since I do, I'm mostly at a point of curiosity and want to trial both.
I'm still wishing I could post pictures, but I think my decision is to get the humidor thoroughly seasoned (7-10 days), and see how it holds before I address the question of sealing the small gaps in the rear.
Bruce, I legitimately spent like an hour going back to try and find that thread of yours again. I can't find it using search, nor is it in my history from last night (which is doubly strange, because I can see my searches for it last night, and other threads I visited around the same time. It's like it's been sucked into the Bermuda Triangle.