A friend of mine kept his R22 in an old lorry back. A standard 40 foot container is not high enough, but certain types of lorry back are OK. You would almost certainly need ventilation though as they tend to sweat inside.
The other thing that is important is to make sure that the ground outside it is exactly level with the inside floor, as otherwise you will not be able to push it over the join on your own if you are using the standard Robbo wheels. I got a set of big wheels from
www.R22bigwheels.com which help that problem a lot. I am considering the lorry back route myself, the only problem is that they are a bit of an eyesore and you wouldn't really want one in your back garden.