deadener is for chumps. Wood, fiberglass and sheet metal is the best and cheapest way to control flex. Spray foam works too. All 100x Better than deadener when it comes to flex. Deadener might work for baby systems but bigger systems require actual rigidity. The amount of money you waste on vibraflex, you could have gotten an even more bullet proof roof with the other alternatives and have more money in your pocket.
Upcoming setup ... two taramps 15ks subs...4 Team Ascendant audio 18s
320 amp singer alt, 6 group 31 agms in the back (clearly not enough)
80 prs, two way active, massive tweets, pwx 10s in the doors, UN 6.5s in the kick on ct 500.2 and alphard 200.4