... if you want a disc rear wheel without the failure problems of the Tioga... just get a set of these for your existing wheels - for £110 + P&P , a bit of stickering and off you go !!!
http://www.raltech.co.uk/Prod_3-Wh-Cov.html
http://www.raltech.co.uk/Prod_3-Wh-Cov.html