I have repaired a few of these, and from what I have found you can't remove the tubes, as the interior is one piece.
The exterior of the case is glued to the interior around the bottom edge. You can easily take the exterior off by separating the glued area and sliding off the fabric. The zipper at the top is not glued, so you can start there and start working your way down.
When you put it all back together, you just need to use contact cement to reattach the exterior to the bottom of the case.
Brian