As you are well aware, the stuff will get everywhere, given half a chance.
My solution has been a separate tent / gazebo type thing.
I use it inside or outside, dependent on size being blasted.
http://www.ebay.co.uk/itm/Car-Shelte...item3f3a4c04ca
Mine has a flap all around the bottom which pretty much seals. Flap is used outside for sand bags to stop it all blowing away!
Dont point the blast gun at it directly, I think it would probably go right through.
Outside, I leave the door open and blast inwards, if that makes sense.
Inside is for smaller bits, so less intense.
The smaller gazebos are just as suitable for small jobs and are a lot cheaper.