Well, certainly remove the valves, wrap them in some bubble wrap, and put them in the back of the amp and make sure they can't move around. Wrap the whole amp in some bubble wrap, and whack it into a box of appropriate size. When the guy shipped me my JCM900 a while ago, he used so much bubble wrap that, when laid out on the floor, was over 3m long! It was certainly well wrapped up, got here safely :)
