I made a case for my M401 out of a plain metal cigarette case, and it took about an hour total. It had metal "arms" on either side to hold your cigs in. I removed one of those by pulling the hinge pin out, removing the arm, and replacing the pin. I then cut a piece of double-wall cardboard a.k.a. corrugated cardboard (you know, like cardboard boxes are made of) into a square just a hair smaller than the case. I traced the shapes of the various pieces I wanted to install onto the board, then cut them out with a razor knife. I only cut
through the top layer, not both, although I think similar results could be achieved either way. Once the holes were all dug out, I cut a chunk of an old sweatshirt about an inch larger either way than the board, then put spray adhesive on both the board and the cloth. I put my cloth inside out, as I like the "fleecy" side better. Once the whole mess was glued together, I used chunks of old pen barrels as placeholders (so as not to gum up my PV parts) and closed the case. After an hour or so it was all dry and I now had a case that held my parts nicely and securely, fit great in my pocket, and looked cool to boot!