A few easy easy questions there mate. In the parcel shelf....Use an Amp for starters, make sure they are securely bolted/screwed to the metal shelf and not the the plyboard (mount the speaker grilles to the plyboard though. Although, I believe in a VC it's just easier to mount the speakers to both plyboard and metal parcelshelf. If mounting is done via plyboard and parcelshelf then no sealing is really needed as the screws will the speakers down against the board making a seal tighter then nuns nasty. If using the parcelshelf only. Then a rubber gasket is ideal, if stuck use a peice of cardboard from the box they came in. This makes a great seal as well.
As for the speakers in the door? If you have excess water coming into your doors. Then you have more problems then speakers getting wet...RUST in the bottom of the doors. Get this fixed before spending money on speakers.
The ABSOLUTE best sound from door speakers is fairly time consuming and I don't recommend doing it unless it's an SQ machine or a Coupe. But, here it is. Get a can of sound deadener and spray every possible surface of the door skin from inside as you can. as much as possible and as thick as possible. Use several cans for both doors if possible (it's not cheap stuff from memory. I get it through work) Next, using 3mm MDF make cut outs for the open sections in your doors and gaffa tape, silicon anything you want but make them stay there! Now, before putting the door skin back on install the speaker and turn the volume up with some bass. See if there is any airleaks around the MDF you just put in. A little air is ok as the door skin will probably put enough pressure to cure this problem. any majorleaks, fix. Except of course for the door lock mechanism if it's in the way, also make sure the door lock operates smoothly. Now put it all back together and wait for people to ask where you mounted the subwoofer? Also, use an amp if possible as well. BEWARE...THESE DOOR SPEAKERS WILL HIT HARD!
