I'm using the wolfman 'wolftail' tailbag. in fact I am flying with it to San Jose tis Friday to pick up my bike from Corbin. The only thing I'd be worried about on the classic seat is damaging the piping visually with the cords/straps. Other than that the bag fits well and lets me change my riding position a bit as I can lean back against the bag. It took some of the pressure off of my tailbone as I rode it all the way up to Monterey for Corbin to pick up. There aren't places to hook it up pre say so I just crossed braced the straps and hooked them onto themselves.
For me, cost is priority 1 and not the amount of function. So I made this work for me for my laguna seca trips from san diego. If it didn't fit, I just didn't bring it! I still brought a backpack.
If money is no object, like it seems a lot of folks on the forum are coming from, then I'd move on.
Below is the link for it from wolfman. I picked it up from revzilla for $89.99 one yr ago. They don't have it anymore, but maybe they'll get it again.