Routers are great for many things however any cutting freehand is just asking for trouble.
Don't let that stop you from creating your own template. I do it all the time and it's a real life saver.
If you have access to a band saw or even a jigsaw (inexpensive and very useful), you'll be miles ahead. Using a full size drawing as mentioned above or even free hand, draw on the template the design you want. Simple use the jig saw to rough cut the template out of 1/4" 6mm hardboard and then fine tune it with sandpaper until the edge is just the way you want it. You will find it sands really easily and you can make adjustments without fear so it pays to take you time here.
Once the template is ready, trace the pattern on the wood you're going to use and cut it out with the saw making sure to stay a few mm away from the line. Next, attach the template to the wood using double stick tape or if you are sneaky, you can use clamps but remember, you can not let the template move at all or it will show when you start cutting again. Finally, use a flush cutting bit with a top mount bearing to smooth the edge.
Remember to work against the rotation of the bit for the best results.
As an alternative, you can use a guide bushing in the router base with a spiral bit to both cut and edge the piece but you will need to make multiple passes so you don't burn the wood or break the bit.. Just remember the template will need to be smaller buy the distance between the bushing and the bit.
Goiks (Nice cases BTW) uses a laser or CNC cut template (Can't remember which) for his cases which is great for production but for the DIY'er, it's a bit over kill. You will need a template however as that is the only way you can maintain control and ensure you have two pieces that match.
Another tip is to use pocket screws. You can purchase a simple Kreg Mini pocket jig for about $21 which includes the special bit. This will give you a very strong butt joint with out using dowels, biscuits or screws into end grain. It will also be hidden which is a nice touch as the screws are installed on the inside for a nice clean look.
Good luck!
