Slab's going to need a Foam Smashing Emoji. Respectfully speaking I will always reinstall the expanding closed cell 2# foam in any work I do. My Champion, I sealed the foam in with Epoxy everywhere I could. Too mush structural integrity is lost unless a much more substantial stringer system is installed to replace the foam which acts to prevent torsional movement and dampen hull skin damage on stickups by providing some backing to the skin between the ribs. Take a look at race boat stringers where they don't use foam and you will instantly understand what I'm saying.