Hi David,
A back box is always a good way to go if you have accessibility and the room for a box. These speakers are designed to work in a wide range of enclosures so it is not critical to have a dedicated enclosure size. So your enclosure size should be roughly double the size of the speaker box it came in. Again you are at the mercy of the ceiling you are installing these in as far as space available. You also might want to pickup some fiber fill (material used for pillows) and use this to tune the speaker once you have built your enclosure. The more fiber fill you add, the more you "fool" the speaker into thinking the enclosure is larger. I hope that helps, feel free to call us for further clarification. There is plenty of information on Google for building enclosures (YouTube as well). Good luck
TL/MA - 1545