No, I don't work for Eastwood and I haven't done my cars yet, but after cutting up my parts can I can see the need for it. Everything is bare metal, (or bare rust) inside. Same goes for the seat mounts and floor crossmembers. You can see that you would need to apply it to the inside and outside. The inside of the rockers and the sill below also appeared to have been bare metal from the factory, (this was '72, my '82 has a black anti-rust coating).



http://www.eastwood.com/internal-frame- ... ozzle.html

Thanks for the product link.