Sorry it's taken me so long to get these posted. Links are posted below. I assume the new forum format does not convert to HTML so you'll have to copy and paste.
Cold_Blooded:
The obsoleta site also has a rack design for rodents.
Dr. Doolittle:
I think the Fine Green Tree Pythons link is the best way for you to see what I mean by a "spacer".
I would not use the box you select as your spacer for a couple of reasons. First, this will make too tight of a gap and second, the box may distort slightly causing your tolerances to be off.
Speckled kingsnakes are not the best escape artists but I think you'll want the gap to be better than what you can achieve by using the box as your spacer. Like I said before, make the gap large and then shim it to your liking. This will also leave more space if you ever have to switch to a new box and it's slightly larger.
http://www.chondroweb.com/fineGTPs/Racks.htm
http://www.arbreptiles.com/cages/rack.html
http://ballpython.ca/The Rack.htm
http://www.kingsnake.com/obsoleta/projects.htm
