I use ProPhoto RGB for processing astro and conventional DSLR images. At the end of the process I convert to an appropriate colour space if needed (e.g. sRGB for web). There's a reasonable explanation of why you might want to do this here:
http://www.luminous-landscape.com/tu...hoto-rgb.shtml
This has almost always worked well for me. The only time it didn't was when I processed an image of the Saturn Nebula. When I got to the end I discovered that the colours in the body of the neb were out of gamut for sRGB and I lost all the subtle detail when I converted
Cheers,
Rick.