hi there,
if u havent fixed it as yet here is what i did with my spongy floor in my fibreglass boat
first i sanded the existing floor then applied maxibond
over the old floor then laid the new floor over the old one screwed it down with stainless steel screws last of all fibreglassed the whole flooor after sanding the new floor painted it & its a solid as a rock
dave
June 2009