I have found that sewing your own bag is not rocket science, somewhat easy to do (just be sure to take careful measurements & allow for a 3 dimensional full shape rather than a flat sheet), and use a good match of thread & fabric for the sewing machine you are using. As for the sort of bag to use for your own, there are many patterns available for you to use for free online. Here is one intended for use on European trains referred to here as a "Housse" (Bike Bag): http://www.mayq.com/Best_european_trips/Housse.htm