[jyl]

Originally Posted by cabmando

Just buy 2x4's the length of the run, cut a notch for the bridging supports and screw the 2x4 to the side of the existing joist at an angle that allows water to flow away and attach your panels. Then as you mentioned, put a gutter at the end to direct the water away.

BTW, have you put a level on the deck floor? Some decks will be pitched away from the structure.

I typed up a convoluted idea but deleted it because cabmando's makes more sense.