The size I recommend is a 4x2x1 enclosure and I personally prefer flip down double doors on my enclosures but sliding glass doors are easier to do when building out of wood.
Regarding heating, I suggest using an ultra therm heat mat from the bean farm. (it is basically a section of flexwatt that has an added layer of laminate covering it to prevent electrocution. And can be placed directly into the enclosure or directly underneath it depending what you want to do) and along with the ultra therm heat mat go with a radient heat panel attached to the top inside of the enclosure to help with ambient and help keep the hot spot high. You will not need a system for humidity since the enclosure will be mostly closed off, but you will need some venting for airflow. You can go several routes for the venting. If you go flip down doors the gap around the door will provide sufficient air exchange. If you go with sliding glass doors you will want to incorporate a vent (I suggest one no larger then 6x3 or in that approximate size range) You will need to install it on the side close to the top. Make sure you get one that does not have sharp edges for the snake to cut themselves on, and also doesn't have any accesses that the snake can push out and escape through.
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Randall L Turner Jr.
www.aircapitalconstrictors.com