You must have a box that states in some way Live harmless reptile for Fed-ex..More over you have to state for the Lacy Act the quantity and species of animals contained within the box http://www.shipyourreptiles.com/en/g.../#question-114
Please read and know all the rules required for shipping..it is a privilege and not a right.
I use a 200# burst rated box and 1/2" close cell polystyrene insulation, if the temps are super cold I won't ship so 1/2" is perfectly exceptionable to maintain temps that are ok to ship in.