Damp in trunk.... on 1996 BMW 328i

Heavy rains for 2 days due to Tropical Storm Issac in north Alabama; trunk mat is damp (not soaked); where could water be leaking in? and what suggestions to fix this problem? Thanks so much for your help.

Asked by for the 1996 BMW 328i
door seals, window seals, windshield seal among many other areas. water leaks are real tricky to trace.