Yes, it is a custom fit!
Markbass manufacture custom-fit bags for
both sizes of head (the smaller, "Little Mark" size and the larger, SD/TA range). The bags even have little flaps that "Velcro" shut and allow you to plug the cables through the back, without taking the head out of it's bag!
Sounds great in theory, but ultimatley it's pretty futile, since the polyester bag would just slide around on the top of any cabinet

hmm: unless it too is "Velcro'd" to the furry cab?)
Also, the price for the small one is
120 Euros 
!!!
That's just f****n' insane! It's 100 Euros more than my laptop bag cost and it has no more padding (and a lot less room for beer

).
OK, enough preaching! I actually hope that Markbass sell a lot of these bags, as Marco deserves to be a millionaire (IMHO). Here's how it looks:
(photo cut)
P.S. The addition of shoulder straps just cracks me up! Maybe they sell a lot to passing pixies!?