Any weight saved in removing the seat will be sucked up in pouring dynamat in. You could just put the seat back in... just sayin'. However, Your best strategy here, if you are sticking with seat out, is to dynamat the trunk floor and spare tire well, which are a tympanum for all the rear noise on these cars.
2014 Premium GT, SGM, Brembo, Auto, Tech, Comfort, etc. GT500s, Steeda UCA, VMP auto N/A tune. 100 shot nitrous on BBR tune. Best e/t 11.42 at 120.64
2012 Premium GT, Candy Red, Brembo package, 3.73, MT82, Comfort, Tech, et al. Procal tune, Roush UCA, UMI poly LCA, GT500s, Steeda red bracket, Hoosier 28x10x16 bias drags. Best e/t 11.91 at 115.23 RIP