[Scatch!]

I've saw one Neon that had so much water in the trunk that it got under the rear seat, but that was an extreme case where the driver either didn't know or didn't care (probably for years). Other than that, the most I've ever seen in a trunk is about .25-.50", but most often the water is so light it looks like the walls of the trunk are sweating. You need to look under the carpet to see this of course. The water will invariably be in the tire well, under the spare tire.

I doubt that a cracked tail light like you described would leak water into the trunk. It would most likely fill the tail light itself first. You'd know it if the light was filled with water...