I have used wood screws that over time have come loose. I'm thinking about tring to find or make a clamp of some sort that will fit over the edge of the sub. Kinda like what holds grills on but a bit more hefty.
With plywood or MDF boxes I'd use wood screws. With particle board use threaded inserts (called "Tee Nuts") which you can get at any hardware store. You drill a hole and insert them from behind, then use machine screws (8-32).
Sealing is important. Don't have any carpet under the speaker's mounting surface. Some woofers even come with gaskets, but if your surface is flat and smooth it should seal OK without one.
mr_unreal, that cooton wool like stuff, poly-fill works by slowing down the sound waves. This makes a small box seam bigger. If you want more SPL I think it would be worth it for the money. Not sure if it is a fire hazard tough.
Use 1 to 1-1/2 pounds of Poly-Fill per cubic foot of box volume.