This is a case for the 2x25 watt audio amplifier board sold by Parts Express (http://www.parts-express.com/2x25w-@-4-ohm-tda7492-class-d-audio-amplifier-board-only--320-332).

Solidworks files are included.

Step 1: Print the two halves. I used 0.2mm layers and 100% infill but it should work with 2 extra shells, 25% infill.
Step 2: Assemble it. Use four 3mm dia, 10 to 16mm long flathead machine screws screws. I used these, http://amzn.com/B000NHTPTC.
Step 3: You can mount it to whatever using some small Pan Head screws.

Note: This case works for the unmodified amplifier board. If you add screw-terminals or whatever then it isn't going to work.