Here's the newest version of the rolling MintyBoost Enclosure. I didn't like how hard it was to install/ remove the batteries, so I revised the design and got rid of the battery holder! The batteries are easier to remove now, and the cost is a little cheaper. I also updated the front pins to hold more securely.
Print out two of the base models- they are symmetric and form the top and bottom of the case. Print off one of the covers. Using Makerware I usually use 1 shell, .27mm layer height, and 15-25% infill (not enough infill makes the pins weak).
Get some battery contacts to hold in the batteries. The part that attaches to the negative side of the batteries is Keystone part number 209 ( http://www.digikey.com/product-detail/en/209/209K-ND/151583 ) , and the pieces that attaches to the positive side is Keystone part number 228 ( http://www.digikey.com/product-detail/en/228/228K-ND/528660 ). You need 2 of each part. You can also scavenge battery clips from old battery holders- they are pretty much everywhere if you look closely. The battery clips have barbs that dig into the plastic and make it tough to put on, so try to flatten the barbs a little with a pair of pliers for easier installation.
Buy and assemble a MintyBoost from Adafruit: http://www.adafruit.com/products/14 (don't solder on their battery holder).
Insert the Mintyboost into one side of the enclosure. Insert the battery clips around the bosses. Solder the positive and negative leads to the new clips. You'll need to solder a jumper wire between the two contacts at the aft of the unit to complete the battery circuit.
Insert the cover into the track, then assemble with the other half of the enclosure. It should be a tight fit! Once you know that everything fits, use the double sided tape included with the MintyBoost to secure the PCB to the bottom of the enclosure.