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Mark - are you always setting up in the same place, or do you move your gear around a lot?
If you are mostly in just one, or a few places, the solar noon/plumbob method works very well, and you know that it is accurate. I never trust compasses unless I know they have been properly calibrated. My father is a sailor, and from memory, he had to draw up tables of his compasses error for each direction. This not only allowed for magnetic deviation that changes at different points on the earths surface, but also for the local magnetic interference of where the compass was sited - he almost exclusively sailed in steel boats, so the interference was significant. I have found compasses that can be up to 10-15 degrees out.
Another method I have used is google maps. Their grid is aligned (I think) true north/south, so you can project that line onto your observing site, and get within a few degrees.
Hope that helps
Adam
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