The best thing would be a corrugated plastic bike box, but seeing as I can’t convince corruplast to even mail me back…
Try getting a regular bike box and painting it with PVA to provide some waterproofing.
Rotors can be left on – cut some [ shapes out of thick cardboard and pad out the gap betweeen the rotor and the spokes.
Bike bags are too small and too heavy if you’re taking a DH bike.
Think – will I be OK to stand the box on end? otherwise you’ll not get it through the bollards at Luton or the sliding doors at Geneva…
I bought a Plasma TV box off the internet specifically for the purpose. (Just the right length for a med SX trail with back wheel fitted, and a bit wider than a bike box for “padding”)