okay so I will foam the inside. Now for glassing what oz should I use so my floor does not cave in. cause that would suck. Using west systems epoxy resin
Did you not keep the section you cut out? You can either bond in the old section, then foam below it (drill holes) or fill the lower section, sand smooth and then bond the tray back.
Might want to consider making the tray a little wider while your at it. Would only bit a little bit more work. Ski would be a lot nicer to ride too.