I have a Genz Benz Streamliner, and struggled to find a case/bag that offered good protection and carrying ease. Initially, I went with a LiteFlight briefcase from Cabbage Cases (Columbus, Ohio). It offered the best protection, but still had to be carried by hand (something I was trying to avoid).
Eventually, I thought of going with a backpack so that I could carry all of my cables/etc on my back with the amp and make gigging a one-trip-from-the-car affair. After some searching, I found this at Target of all places: http://www.amazon.com/Swiss-SA-9275-...ref=pd_sxp_f_i
It has an interior padded pocket with a velcro strap that is exactly the dimensions of the Streamliner. (It took a little coaxing the first time i put it in, but such is life...) It has adequate padding for getting to/from club gigs, and would work really well as an airline carry-on, too. Plenty of space for cables and other gig-junk. The way that the bag is constructed, the amp pocket doesn't actually touch the bottom of the bag, so if it were dropped, there would be a little space between the amp and the floor.
Not sure if it would work with other small bass heads (especially ones with sharper corners than the Streamliner), but nonetheless, I highly recommend it.