I had the same issue on my Xpress, if you moved your foot or stood up on the deck it would cause the holders to wobble and with 16' rods a little wobble at the holder would make the tips move like crazy. My problem was because of the compartment hatch being in the center not allowing the hat channel to go all the way back to the back wall were it could be welded in.

I took a piece of 2x2x1/4 aluminum angle and placed it underneath my pedestal mounts using the existing holes with new longer bolts and tied all 3 bases together, doing that "sandwiched" the two runs of hat channel that were not welded in and gave them some support.
IF I could get underneath there I would add another closer to the front as well but I can't fit in there!