I use the 12x9x6 for the ball pythons up to sub-adult size.As far as the delicups or bags its up to you.I punch a hole on each side of the box for extra air,as long as your snake are secure in the deli containers or bag they can not escape.The heat packs are for cool or cold weather and the cold packs are for hot times of the year,you do not use them both at the same time.Originally Posted by jwk811