they don't call what you need rubber boots. Actually what you need is a speaker baffle. They still make them out of a waterproof foam and even out of plastic. they improve the sound greatly and they are cheap and nothing gets into them. here is a link for just one place that you can get them. I would recommend the foam ones not the plastic. i used them with my door instal and they were perfect no water or dirt gets through. look atthe picture too see how they work.
http://www.autotoys.com/x/cust/produ...productid=5412