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warshawlawwe don't have basements, so we never get sump type flooding. I store 'em in plastic holders (mostly top loaders with sleeves inside) in plastic tubs up high anyway. LA would need to be under 7+ feet of H2O to affect them. You need to look for a positive seal with your storage tubs; by that I mean a condition where water will not get inside the box without flowing upwards against gravity. Think lids with lips that overlap the box sides.
We do get earthquakes. My collection rode out the 1994 Northridge EQ without a single ding, in a home that was completely destroyed, because I am such a bug for holdering.
You might also consider insurance.