Another place (sorry if it was already emntioned) is the cowl area. This is a great place for mice to build a house. When the center cowl drain backs up from debris, water can pool in the inner cowl area. It can manifest itself when it rains/wash the car you'll get water on the floor of the car. Also, sometimes if you look under the hood you may see rot hole on the firewall near the mastercylinder. Not particular to convertibles, but any car.
