I just wanted to let you all know that I finally found a backpack for my Gallien Krueger 150 MBS. It's the North Face Base Camp Duffel Bag -- basically just a large duffel with backpack straps, and it's the perfect size for the GK. Here's a link to the North Face site:
http://www.thenorthface.com/opencms/...1D&language=en
I put a half-circular piece of closed-cell foam in the bottom so that the amp's sharp corners don't damage the bag, and I put the amp in upside-down to further minimize pressure on the corners (the GK's top corners are recessed). I got it from Paragon Sports on Union Square (Manhattan), and the only drawback is the price ($110 retail).
This will make gigging in NYC with my amp MUCH easier, since I won't have to deal with those crappy little carts any more, and I'll have both of my hands free for my bass/doors/metrocards. Plus, I can also use it as an awesome duffel bag. Highly recommended!