I did the same thing with some bracing to stop that ribbing of the skin panels.
One issue I had was with the cut outs for the snorkel.
Check the deck fit and its alignment with all the former cutouts.
I can't remember what and how I adjusted things but I remember an issue with all that area.
I had to shift the slots in the deck or in the formers or somewhere...?
Maybe theres something in my build thread?