WHAT?!! dynamat cracking?!....yeah...right.
that'* a first for me to hear. and why would you think to not use it if you have a really expensive system? That'* when you'd need it the most. Dynamat is a rubberized sheet that acts as a weight on surrounding surfaces to stop vibration, and also to block sound-waves (somewhat.) In fact, I would also put a layer of it on the inside of your doors, and some on the door panel. It cuts down on distortion and resonance for mid-range speakers. It will make them sound warmer, and overall much better.
Dynamat is going to help your trunk a lot. I'd do a layer of it on your entire trunk, and extra layers in places that rattle more than the others.