Corns are great!
A 29 gallon should be good for life. Make sure you have a temperature gradient in the cage-you can do this by getting an undertank heater (most pet shops sell them) and sticking it under the tank on one side.
If you use a substrate like aspen mulch, make sure to feed in a seperate container or on paper towels to prevent the snake from ingesting the mulch.
Make sure the tank cover is immposible to escape, if there is the smallest opening the snake will find it and exploit it.