yeah i agree the bottom is the key. that thing is heavy and needs some beefing up to send it out.....plywood is a good idea. i haven't seen that done before, but it sounds good. got to remember that.
i have had 2 shipped to me. 1 useing a 5 gallon stain bucket, the other useing a milk crate. both held up pretty well. the milk crate maybe better if it is reinforced a little on the bottom.