Most adult males will be fine in a 4x2. Some get too large, but for the most part they'll be fine. There are commercial racks made for larger species. You can see some in the "Big Snakes" episode of snakebytes.tv. Sterilite makes locking tubs that should work alright. That plus some bungees should keep him secure. I wouldn't recommend actually keeping him under your bed though. If there is an electrical issue that causes a fire, you don't want to be sleeping on top of it.