Citing Materials from Archives Is Not for the Weak of Heart

Today I have been struggling with the skimpy guidelines provided by the Modern Humanities Research Association that tell you how to cite materials found in archives. I’ve used Chicago and MLA for this in the past, and gotten quite a few migraines trying to get the citations just so. But these MHRA guidelines are really not too fleshed out. Anyone out there know of a site that explains more fully how to interpret the MHRA rules?