definatly double box.
first. the neon needs to be wrapped tightly in a foam or bubbles and then needs to be packed in a box. after that put that in a much larger box with lot of packing peanuts making sure there is no space left for it to move at all.
if that seems too hard, try UPS or fedex. I believe UPS will pack it for you with a guarentee of some sorts.
good luck