Feel around the carpet under the dash and elsewhere for wetness - in the trunk too. It takes a fair amount of water evaporation to make the interior glass sweat. Leaks are common from air the conditioner and places around the windshield, as well as the trunk. This can make the carpet or insulation damp up by the firewall.
Put it in a garage with all windows open and a fan blowing through it to dry it out.
