Under dash speakers mounting advice needed

[Lippyp]

I have just been out and bought a pair of JBL 4" 425E 2 way speakers to add to my current Panasonic CD player in my truck. The previous owner fitted two Pioneers in the back corners of the doors and the sound is muffled by the seat (and possibly my butt!. I also have some better Kenwoods to mount in their place. I'm not looking for huge bass just better and clearer sound than I have at the moment.

I want to mount these 4"'s in place of the stock speaker up under the dash so they are out of sight and high up. I know this has been done before (I think it was by a board member called Greasemonkey), and I wondered if anybody had any pics of a similar install or any advice. I was thinking of mounting them on some thick MDF with appropriate holes cut in it and then putting a rubber seal around the top to stop any rattling aginst the dash. Any suggestions on what I can then attach the board to under there (I haven't looked yet)

Question for the audio guys, should I remove the vinyl from above the speaker apetures and replace with an acoustically transparent cover?

Any advice/picture gratefully received.

Thanks