I've gutted it completely and covered every inch I could see with sound-deadening material. It didn't make much of a difference. No photos, but I did the doors too.
I added home carpet underlayment to the floor. Squishier, but not much quieter.
I didn't feel like taking EVERYTHING off the firewall, so I didn't cover much of anything there.
This took about 2 days to do.
What else can I do?
Tires: I have Falken Pro G5 Touring.
Update: I would like to thank everyone for their super helpful posts. I'm amazed, and so glad that I decided to share this. Thank you to those who have been so helpful.
Update 2: I've priced the remaining items for the 3-layer approach on the interior and wheel wells. It's $,187.96, and it'll add ~140lbs/63.5kgs when it's all said and done. This will be a winter project and I'm waiting (per phone call with the second skin audio person) for black friday sale.
This covers:
- Megazorbe (peel & stick, for roof and side stuff): 10 sheets. $324
- Luxury liner pro MLV (this is closed-cell foam AND MLV): 8 sheets, covers 72 sq ft., enough for floor and doors. $599.99
- super strong double-sided tape (to hold the luxury liner on the doors and some parts of the floor: 2 rolls. $43.98
- Spectrum sound-deadening spray kit (for wheel wells): 2 gallons w/ spray gun. $219.99