Waterproofing Maps

Ryan said from another post:

I like the Rite in the Rain paper for writing, but for map printing, it's expensive and heavy. So, I like regular copy paper: cheap and light. When I'm done printing, I usually go one step further, hang the maps from a clothesline, and spray them with Rain-X or Scotchguard.

I have always used Thompson's Water Seal on my photocopied maps. One negative is that they can become translucent. Does Rain-X or Scotchguard do the same? What do you use?