Previous house I lived at the bottom of a hill - pit was bone dry - mild steel stored in it did not go rusty.Reason I asked is that my neighbour has an inspection pit, and quite a bit of water seeps in. Consider putting in a slight slope in the bottom of the pit towards a small sump recess in a corner to trap water, oil, or other fluids; it would make clean up much easier.
This house, top of a hill, I had to use tanking slurry on the bottom 2ft of the pit, despite it being built in a visqueen bag . . .