Flats are deffo the answer Keith. I made a simple light box from foamcore board, tracing paper and some leds which works very well. A better idea is to use halogen bulbs which are pure white. The thing with flats is they must match your setup. If you set up/strip down then you must take the flats every night. Nothing must change between the flats and the image. Camera position, focus (not so critical), dust. If you can exactly re-position the camera and you know you don't have any extra dust donuts then by all means re-use flats.
I always take flats with the average adu (peak of the histogram) just above the midpoint (about 40000).
  