I cook all my meals before dehydrating.  It goes in the dehydrator at the point when it's ready to eat.

While I don't prep meat for tripping, I know those who do and they use the same method.  Make the whole casserole, except the noodles.  Dehydrate.

Things dry out better after they've been cooked.  Cooking breaks down the cell walls, releases water.  It also rehydrates faster/better.

Russian Fluff sounds like Beef Stroganoff?