I used a lot of foam, almost too much.. After filling up my trunk lid and some gaps in the fenders/wheel wells I was doing some wiring weeks later and found that the foam filled pretty much my entire unibody running from the trunk through the rockers to the firewall. Only time will tell how combustible that stuff really is
And make sure you wear gloves.. I won't even get into the horror storys trying to get that shit off my hands.
As per the conclusion... I will foam my next car, It works great.