How am I going to do this?

[JAKES 68GMC]

I have a Alpine CD player that I want to put in my truck. I don't want to cut the dash all apart to put a stereo in, so I was thinking I could mount it under the dash like a CB radio. But I have one big problem, the radio has all the vent holes in the back part. If I mount it under the dash, that would be a good chance to get some water in it.
So my question is, are there any plastic, metal, or fiberglass boxes out there that will keep the water out? Not completely waterproof, but something to just cover the holes up, or will I have to make something? There are those plastic waterproof enclosures/boxes for boats, but I don't need anything that bulky. The players fits good right where I want it, my knee doesn't rub on it, and I can change the station quick when Pink Floyd or Elton John come on, but can crank it up just as quick when theres some AC/DC or Skynyrd playing. Any and all input would be helpful.
Jake