I recently contacted SEWFINE and was told that indeed they do have a patter for the vanagon seats although it is not in their catalog...I believe they are rather pricey though... They are supposed to be sending me their catalog so I can look at materials/ prices.  You may want to look into them as well. 
1-800-739-3463 (Lakewood CO.)

>>> Alain Thibault <alain@INTERGATE.BC.CA> 04/04 2:19 AM >>>
Hi
Has somebody covered his seat in his van. What company and/or model of
seat covers would best fit the Vanagon seat (swivel seat and the back
seat).
Thanks
Alain Thibault
Westfalia 1991