I keep my 6ft JCP in a 3x2x2 cage. If you're planning on getting a coastal, I'd get a 4x2x2 cage. However, Anthony Caponetto (ACReptiles.com) keeps most of his adult carpets (even coastals) in 36x24x15 cage.

My JCP rarely goes to the left side of the cage; he's always hanging out on the right. I'm pretty sure he has enough space.

Jungles are definitely climbers. I wouldn't call them arboreal, but my carpet spends 75% of his time perched or on his shelf.

Not sure what size tub they need, I wouldn't like to keep any carpets in racks.