Just out of curiosity (and I know this is way off topic but bare with me), how much bondo do you usually end up using when you smooth a firewall? How thick of a pass of bondo is acceptable for something like that? I lined mine all up and spent A LOT of time making sure it was straight and I have made sure to tack around the edges rather slowly to avoid warpage. Well, it warped, I don't know how I ended up doing that.
How do you avoid warping such a large flat area?