I was concerned with the cypress mulch (what I called Eco Earth in my previous statement) as well honestly and when I switched to Reptile Prime is when the snakes started burrowing and I thought that was the coolest thing.

You can also find the black plastic hides on Amazon, that's where I got mine from.

You are correct, some people say the large enclosures will stress the snake but in my VERY HUMBLE and NOT an expert by any stretch of the imagination opinion, if your temps and humidity are on point, and you provide plenty of cover the snake should be fine.

As far as tub sizes are concerned, I do not use tubs (except for my baby Brazilian rainbow because I'm concerned about him being between the glass of a T10 right now). I keep him in a small tub in half of the T10 for now....

Good luck - you'll find a ton of knowledge here.