Another option for sound proofing:
http://www.b-quiet.com/

And another tip - most of the road noise in my Insight was coming from the rear well area.
As an experiment, I borrowed a heavy down comforter from the bedroom and spread it out over the cargo area, and was careful to not block the vents. Next commute to work I noticed this considerbly reduced the road noise. So I only put sound deadening in the spare tire/cargo well area.

Regards,