assuming you have a hatch, this is a prob that like 75% of 240/180s have <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/sad.gif" border="0" valign="absmiddle" alt='
'> usually the water comes in through one of the tail lights.. you can test by pouring a small cup of water through the gap tween the tailight plastic (on top) and the trunk's body metal, take off your interior cardboard/carpet stuff inside by the tail lights and watch for where the water gets it... then get a calking gun and some silicon sealant and go to town <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt='
'>
If it persists, or you don't have time to deal with it right away, be sure to take out one of the drain plugs in the trunk, there's one in the spare tire well, I just left mine out.