If you need a large, sturdy box, get a box from a bicycle shop, then cut it starting from one corner to fit the tripod's dimensions. You'll end up with multiple layers of 3 layer cardboard protecting it, add foam or bubble wrap as needed for cushioning.
But, as mentioned, tripods are not especially fragile, except for it getting scratched up, and knobs coming off, you could just as well paste a shipping label on one leg and send it off. If you have a tripod that isn't up to being shipped with minimal protection, you probably don't want it anyway.