I have floors in my car. Put them there last winter.. But I also have several leaks, air and water seem to flow through the car with relative ease... Any good thoughts as to haw to seal up body repairs..

Try a seam sealer such as the one that Eastwoods sells.

It is a pliable non-hardening sealer and you can put it on with a caulking gun. They also have a brush on sealer that is 19.99 a quart.