I'll second the fluorescent light tube. I use some to convert a damaged Semroc Goliath into a night flier. The Goliath uses ST-16 tube, which is a couple of thousandths of an inch larger than a BT-60, and it only took a bit of masking tape to make a snug friction fit.

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John Buscaglia
NAR 27366
SAM 63
CMASS Member