Just to go against pretty much everything the others have said...
These are what they've got 8 of out the back at the Buccleuch -
http://www.asgardsss.co.uk/motorcycle-storage
They're very, very good - doddle to get the bike in and out of, watertight yet ventilated to prevent condensation and rust etc.
Size-wise - I've had my SV & Blade in the standard one, Fallout's fully loaded Tiger goes in there fine too - unless you're planning on swapping for a Goldwing any time soon I'd say that one would be fine. Larger one would let you stick the kid's push-bikes etc in there too.