Well with only 3ft long - unless you don't plan to move the light - its going to be very difficult to have ducting set up. They are very close to 3 ft long and on top 6" in diameter. If you just have it set up so that the light is at the top you might be able to get away with setting it straight into the wall/sides. That will help a lot to cool with no ducting too.So a cool tube around a 400 watt makes a huge difference then?