Ray,
The more I think about this, the more I wonder why you wouldn't be better off using a 4x5 with film. If you are routinely shooting exposures in the 30 minute-plus range, you will shoot very few frames, and can't exactly "chimp" for exposure, etc. If you nailed your reciprocity tables with your film of choice, you could enjoy the quality of 4x5 and the benefits of movements, etc.
Also, since you wouldn't have to wait through dark-frame subtraction, you could, ironically, shoot twice as much as with digital.
Just a thought.
-N.