Thanks for the kind words. The HRSI tiles are from the Cutting Edge decal sheet, but I darkened them and tweaked them a bit; Columbia had extra HRSI sections on the tip of the tail after the SILTS pod was installed, and there are some black LRSI tiles on the wing glove. The Cutting Edge decals are great, but they need to be darkened somewhat, especially in 1/144th scale, in my opinion.
The base? Funny you should ask. The white thing with strange holes in it is just a spare piece of wood I use to cut things on and I use it as a backing when I drill holes in other things. That's why it looks ratty. The model's "permanent" base is a small picture frame with a mirror installed. A piece of brass tubing is attached to the frame, and it fits into a small hole in the belly of the Orbiter. That way, the viewer can see Columbia's underside. So far, my meager abilities with a digital camera have prevented me from getting a truly decent photo of the belly.