To pump a little life in to this old thread. Tile would be fine, if you want to add fourty pounds of tile, grout, and mortar. If you want to go balls to the wall then:
Build box as usual
use acrylic fortifier instead of water to mix your mortar(thick pancake consistancy)
1/4" trowel to apply mortar
place tiles
You can install them on as many as five sides at a time depending on designs and size of the tile
Use epoxy gout as it will hold better(difficult to use, until you learn)
I wouldn't test the box for about a week to let everything cure properly.
Any tile questions, let me know. I own my own business.