About driver mounting, you can always increase baffle thickness or to add "meat" in the places where the screws will be placed. One can add material just where the screws will be or a thicker panel can be used for the whole front baffle. Sure can't hurt.

As for gasket material, Eminence cone speakers come with a thick paper gasket both on the front and rear mounting surface and JBL parts come with a large O-Ring for the rear and a gasket for the front. Honestly, I prefer that these be the only gaskets used, and I like to use them dry. That way, if there is ever a need to service, it is not a messy affair. But this requires some dilligence in cutting the right size hole and having it cut perfectly round so that there is sufficient sealing surface.

I like to run the speakers at a loud level for a period of time and feel around each joint for gusts of air. The most common places to find leaks are around the drivers and horns, but sometimes you'll also find them on amplifier connection panels or even at corners of the cabinet. If one finds that a seal isn't adequate, then gasket fill material should be added.

I've found that caulking material works well in these situation. My favorite is the non-hardening "tar-like" material sold by hardware stores and even places like Parts Express. But you can also use a silicon gel that cures non-pliable just as well.