You'll get more lighting bang for your buck with an agricultural light. A T5 flourescent fixture is great and runs real cool, search user 'kdspecial' for an all- T5 grow that yielded very well. Even a smaller wattage HPS such as a 150 or 250 can be found reasonably cheap- check Inside Sun.
Instead of a small rubbermaid, a piece of actual wooden furniture like a bureau can be more stealth and easier to keep cool- more interior space to work with is in your favor, and drilling holes in the back to install exhaust and power cords is easy.
Remember that with a HPS or MH, you need about a 2x2x4' space MINIMUM for the smallest HPS practical, like a 250. Even that is pushing it.