Water in trunk after heavy rain

I have a 74 dart as well and have the problem but traced it to the seals in the rear tail lights.
http://www.ebay.com/itm/290376623899?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I also had a vynal top and when it is removed shows just how bad they rot at the bottom of the rear window. Try spraying water at your tail light and tell me they don't leak. I'd be surprised if that isn't part of the problem since water drains right down the trunk channel onto the light bezel. The water then traveled to the front of the trunk.