Hi Glenn. I just caulked that first space between deck boards, and only for about 15 feet. What I may do is remove the deck board closest to the house, and then pry the bottom of the siding out a bit. I could then insert an L flashing behind the siding. I could put a 1/4 inch downward bend on the other arm of the flashing. I could make a small notch in the joist, and insert the bent portion of the flashing into that. This would be to stop water from running along the top of the joist into the house. What do you think? Thanks, John.