As someone whos been into top end sound quality ice since the 80s (also a member of talkaudio for toooo many years and moderate a forum of the world champ) i know what you meen about the road noise.
Dynamat is not strickly speaking a sound dampener its a resonator reduction device. It basically adds mass so changing the resonance frequency of the panel reducing the noise that way.
Its good to RTA(real time analyse) the frequencys that are the issue and then try and find them using the mike.
The 3 door suffers more because the sound comes in from the rear quarters.
VW use to, but don't know if they still do, fit a foam in a plastic bag over the rear arches on 90s polos i used these on an ibiza i had which helped a large amount. Nothing stopping you making your own out of closed cell foam.
You want sound absorbsion not resonance reduction so you want some closed cell foam for the arches floors and boot floor.
A couple of things i found that helped a very small amount was fitting the TT back bottom arm cover but it was such a small amount but makes a difference when its raining.
Another thing that helped a tiny amount was my rear wheel arch inner covers i resealed with more water repelent, so behind them inside the arches stay totally dry. I know a trick some car manufactureres do to the press fleets is fill this void with closed cell foam reducing road noise.
Also try altering the tyre pressures i found using 36psi the same as what the mk5 used.
