Blocked Rain Drain/ Coolant leak?/ Avg. 99 Life?

[DianeVB]

I have a 1999 Boxter, purchased used a couple of years ago, mileage about 60K. It is parked on my drive, so it is kept outdoors. The problem is when it rains very hard, the water stays trapped in the car! Driving along cross streets, stopping every 300 feet, I can hear the water "sloshing" on the passenger side as I come to a stop, then the same sound again as I accelerate. If the rainwater drain lines are blocked, could it be from the top of the drain, or as well from under the car? If it is clogged with leaf debris, what must I do to unclog it? I had taken the car to a repair place because coolant was leaking, and I also told them about this problem. They forgot to take care of the drain lines, and I told them not to bother when the tech was going to go at it with a coat hanger. That made me nervous, because I was thinking that the line could be a hose that I didn't want punctured. Now we've had a second deluge, and water is seeping into the passenger side floor carpet at the outer edge. I have never had any car with this problem. Also, today the car temperature gauge seemed to be creeping past the 180 to the right. We just had a new coolant tank installed - very expensive. Any advice??? Reading about the IMS engine failures is very concerning. Any stats on the average life of a 99 Boxster? Thanks!