Nearly all of my radio is done portable in one way or another. When I am car portable like many people I bring the cables in through one of the car windows. As I like to operate both through the winter and in the summer I wanted to keep the cold and rain out in winter and the flies out in the summer.
My simple solution to this is a strip of 1 inch thick closed cell foam with a shallow slit in one edge to fit on the top of the window, and a notch for the cables. Simple but works for me. It also doubles as rattle reducing packing on the way up and back!