Here's some DIY Bow cases, might give you some ideas,
http://www.archerytalk.com/vb/showthread.php?t=2058759&highlight=case
http://www.archerytalk.com/vb/showthread.php?t=2085897&highlight=case
http://www.archerytalk.com/vb/showthread.php?t=2095975&highlight=case...