I store liverock in a 300 gallon rubbermaid stock tank. The tank itself is 25 inches deep and the lights probably hang a foot or more above the tub.
For lights I use two double shop lights from home depot with two regular daylight bulbs from home depot.
The key is excellent water movement and keeping up the calcium and alkalinity. I use rio 3100's for circulation. I rarely run a protein skimmer.
You'll need to drop some food in the liverock container every once in a while to keep the bacteria going. Without anything to process, they won't be around for very long and it will also help populate the rock with lots of tiny critters like pods and stars and the like.
If you're using such a small tank to keep your rock for a while I would go to Walmart, Home Depot, Costco, or a similar store and buy the lights of america 65w PC floodlight. It's like $19 and has a full spectrum daylight bulb. Sometimes they don't come with power cords so you'll have to wire one in, but they would be excellent to keep your rock.
Don't over feed the tank. A tiny bit of food is enough every once in a while. Remember the cal and alk. It's still a tank so top offs are necessary and water changes as well.
Good luck. | 
