I would not plan for more than a year and a half for a Carpet in a 29 gal. It depends on the snake, could be less or could be longer.
Most can end up in a 2 x 2 x2 if you are limited on space. I have a 7 footer and an 8 footer each in their own AP T-25. That is a 6 x 30"W x 18" H only because I have the room.