I'm big on the tubes as well, for the organizing and auditing reasons given already by others, not to mention the fact that they are useful--or even required--for some games; e.g. "barrier reefs" in Armada, the "golf club" in Penguin Golf, the "Moon's gravity well" in Moon Shot.
That said, a combination playing board and drawstring bag *is* very clever. Perhaps you could use the reinforcing second fabric layer/backing for another board layout--say, three-way or five-way Martian chessboard--rather than using plain fabric?
For my own storage, carrying, and demoing purposes, however, I have found this particular case-binder to be PERFECT:http://shop4.outpost.com/product/5033875
First, it is tall enough to hold 11 tubes, with just the tiniest bit of "shift" of the 11th tube. It doesn't QUITE lay flat, unless you reorient 6 of the tubes the opposite way to account for the wider tops than bottoms--I don't reorient because I like all my pyramids to point the same way and it's only, like, a half a millimeter off. The only thing you have to do to "prep" the case-binder is pop off the locking three-ring binder unit inside of the case: I did it with my bare hands, so a small pry bar would be the most that anyone would need to bring to bear on the task. I left the rivets in the case to help maintain water resistance, but you could pop them out with decent wire cutters, if you don't like the slight bump they make on the bottom (barely noticeable, once packed up).
Second, once the tubes are laid flat in the case, there's about 3/4" of additional thickness and about 2-3" unused on the side. Enough to hold a set of Martian coasters including the black one, 6 laminated Eeyore tri-boards, 2 bandana chess boards, a Volcano board, a crackled CD, Playing with Pyramids, a printout of 18 more games, a small Crown Royal bag containing about 80 Zendo stones, 10 poker chips marked for Homeworlds, a Morgan-Greer Tarot deck, a pen, 6 dice, and a small stack of mini-catalogs. In short, I can play just about every pyramid game on the wiki by carrying around this one case-binder.
Third, the clip on the cover of the case-binder is great for holding a few catalog brochures or a piece of paper for tracking tournament or demo activities. Decorate the boring pewter-colored plastic with cool stickers and you're good to go. It might even be paintable, with the right type of paint or plastic dye.
Hope this helps!