Checkout the following articles from the "Projects and Articles" section:
Modifying a Newtonian Tube for DSLR Photography
http://www.iceinspace.com.au/63-441-0-0-1-0.html
Astrophotography with a Dob
http://www.iceinspace.com.au/63-201-0-0-1-0.html
Folks I know who have purchased or made an Equatorial Platform for use with a large Dob have found tracking good enough for visual astronomy, but not very good for long exposure astrophotography of nebulae, galaxies etc.
- nowhere near as accurate as commercial German Eq Mounts
- lacks goto capability for helping to find faint fuzzies
- no input port for closed loop autoguiding
But it does sound like fun, and should work better on the NT than it would down her in Melb at latitude 38deg south.
Cheers,
Jeff