I thought I would share these here as well because cardboard boxes suck, here are some ready to print 32x cover inserts! They are formatted for Universal Game Cases (UGC) and standard Sega clamshell cases. For optimal results, you should print them from Photoshop to avoid the images getting resized.
Note: 32x games don't always fit very well into Genesis clamshell cases, however there are 4 Acclaim 32x sports titles that came in plastic clamshells designed to hold a 32x cart (NFL Quarterback Club, NBA Jam & 2 WWF games). Also, some Genesis cases have a slightly larger cartridge holder that can accomodate a 32x cart quite nicely.
After Burner
UGC cover: http://www.box.net/shared/0s9hseepav
Sega clamshell cover: http://www.box.net/shared/zxs6vp0dxe
BC Racers
UGC cover: http://www.box.net/shared/d1hfajsnaf
Sega clamshell cover: http://www.box.net/shared/kpxpx22syh
Blackthorne
UGC cover: http://www.box.net/shared/0zh31jhirp
Sega clamshell cover: http://www.box.net/shared/tx005pg7sk
Brutal
UGC cover: http://www.box.net/shared/1kib9kjo4i
Sega clamshell cover: http://www.box.net/shared/myyptbhron
Cosmic Carnage
UGC cover: http://www.box.net/shared/91xb8cs8if
Sega clamshell cover: http://www.box.net/shared/jispflyrj9
Doom
UGC cover: http://www.box.net/shared/knt0k959c1
Sega clamshell cover: http://www.box.net/shared/7k4cqqpbkc
Knuckles Chaotix
UGC cover: http://www.box.net/shared/cto9aqnj2o
Sega clamshell cover: http://www.box.net/shared/3ff6vddijf
Knuckles Chaotix (Japanese art variant)
UGC cover: http://www.box.net/shared/s9yqeu17qn
Sega clamshell cover: http://www.box.net/shared/uni92gip72
36 Great Holes
UGC cover: http://www.box.net/shared/66p081g4zb
Sega clamshell cover: http://www.box.net/shared/t24g21v84v