i was thinking about this, this past weekend. I have dont this to a Fender 4x10 blues deville, i turned it into a "head", although the verticle chassis is very tall, so it was not so compact.
What i did was basically strip the chassis, cut to bottom, removed midddle space, then dowel rod up the top and bottom, glues and set. I also added some internal corner runners ( think a 1"x1" piece of wood that follows the inside bottom corner and is screwed into both the top and bottom. You see this a lot is crappy box contruction, but it, plus the dowels, created a pretty solid construction. Prob the most dificult think would be cutting the bottom, and removing the middle evenly. If you dont get it so even, you will just need to add time for sanding, but you can get it spot on with some effort. If youd like, you can even leave to bottom feather joint. What i mean is, rather than cutting off the bottom so you have just a board, you cut about 2 inches from the bottom, so you are left with a bottom piece that is really a "U" shape. you can then certainly dowel that to the top, but you might want to add some interior bracing.
For the dowels, there are many companies out there that sell ready made jiggs, so you can line everyhting up easily. usually they will sell a kit that is made just for 3/4" board...just look for a kit that makes sense for your application. you just line everyhting up, make marks, place in the jig, drill the hole on both boards, set with glue. Some wood glues are solid as a rock.
Dont know how into wood working you are, but i hope what i offered helps. Also for recovering, i have tried tolex glue, as well as spray off adhesive, and i ahve to say the spray off has always worked better for me. 3M super 77, you just spray and lay! any overspray comes up immediatly with mineral spirits, even after it has dried. Tolex glue just takes to long to set up. Also, once you staple the edges, it does make to much difference.
