Hola Dave,
Take all aluminum floorboards out of sib, inflate keel to 4 psi with a gauge, pour soappy water all around keel to see exiting air bubbles to spot leaks, probably whole fabric no good due to much mini abrassions against under alum floorboards and lot's of bubbles outting. In that case will need to replace complete keel. Also check air valve, pour soappy water inside as well and see if there are bubbles.
Alum floorboards should not pop out at all, 3 issues: (1) maybe you're under inflated, all sib chambers must be inflated to 0.25 bar or 3.5 psi for correct engine/sib performance, (2) maybe lateral alum side joinners are at a (incorrect position) thick flat portion must be on bottom floor fabric or (3) a combination of both (1-2) issues, check.
How much $ is a Zodiac new keel ?
Happy Boating