The only way to truly know if an amp is clipping is to get it metered with an O-scope.
Clipping like has been said is not always audible and when your amp is clipping or even
the signal its receiving from the H/U is clipping its disastrous to your equipment.
This is true for most subs, but some do not it depends on what you bought.
That weather stripping will work though just lay it down and make sure its even the whole way around.
Then make sure its pre-drilled, and slap it in. No sweat