Butyl sound "deadener" only deadens the sound level but doesn't absorb or block sound. Deadener work well for resonance frequencies on larger areas that aren't reinforced. 30% coverage makes 90% of the gain and the rest is mostly a waste. However for sound blocking you need 100% coverage. This requires mutliple layers, deadener, usually a foam blocker/absorber and then something like mass loaded heavy vinyl. The mass loaded vinyl is HEAVY and does most of the sound blocking, the deadener and foam kinda just help with the resonate frequencies and muffling/reducing the sound before the mass loaded vinyl. Foam also does great with insulating and blocking heat transmission.
I've had decent success with multi layered products like Siless 2in1 and 3in1. Unfortunately they are made in the Ukraine so its hard to get. I had zero insulation in a 87 firebird which has a turbocharged LS and large 4" exhaust so the car is not quiet and has a race suspension. On the street you hear everything and heat in the summer is brutal. I used the 3in1 product which is .050" butyl, 1/8" foam and another 1/8" or so of heavier foam with foil on top (basically 1/4" thick). I covered basically 100% of the firewall back to the trunk and then replaced the carpet with one that had mass loaded vinyl as part of the whole bottom of the carpet ($500 carpet). I got 2 boxes of 36sqft of the 3in1 and used about 3/4 of it. The difference was very noticeable sound and heat and worth every penny. I also tape my edges with fiberglass foil heat tape on this car bc of the heat from the exhaust and proximity to the floor pan.
On my 2018 CC Laramie I opted for the 2in1 which is .050" butyl and 3/16" foam (couldn't get the 3in1 due to the Ukraine war). I was getting resonance from the catback exhaust. So I yanked the rear seat and pulled the carpet up from the storage bins back up the rear cab wall. Covered almost 100% with the 2in1 and put it all back. I also have the stock Apline sound system with JBL speakers, Pioneer shallow sub in the stock box and I built a custom fiberglass box for under the pass rear seat and have a kicker 8" shallow sub with an apline 300w amp. The 2in1 did deaden the resonance a good bit and I plan to the rear floor and rear doors in the future. The difference wasn't as dramatic as the firebird but thats because the vehicles are much different in sound and ride quality. basically what I'm saying is just doing the butyl will make a noticeable difference but if your going to do it I would opt for more than just the butyl. Adding a layer of NEMCO foam deadener off amazon would help further or going with mass loaded vinyl for even more sound blocking power. Mass loaded vinyl can be $$ though! I used a dB meter app on my phone to verify my findings. I also believe it helped with my sound system getting a better deeper bass which is hard with the smaller 8" subs. I heard doing the doors makes a big difference so this spring/summer I want to try to attempt that.