Hi John,
Perhaps a step up from garbage bags (not that there's anything wrong with that
, ), you could try 14 inch /350mm spiral duct or one of these (unfortunately 18 inch) tunnels....
http://www.ebay.com.au/itm/Kids-Chil...QAAOSwOdpXzlTR
http://www.ebay.com.au/itm/5-9-Feet-...0zjgmfhZcdcfNQ
Of course it would be better in Black (paint or dye it? or look a for another) and it's a little large at 460mm, but perhaps you could upgrade to an 18inch
Best
JA