Sealing the backseat aluminum plate from the trunk area.

Race Fans ,
After installing the cage in my Duster I have yet to find a way to "seal off" the gap in my aluminum plate / Trunk area from each other. Knowing safety is of the upmost importance as there is NOT A REWIND BUTTON as one does not get a second chance when a wreck happens. No one wants a wreck to happen but this is where the correct preparation comes into play. I am still trying to figure out a way to seal that gap between the body and the aluminum plate I installed between these two areas them keeping any possibilities of gasoline coming into the driver area.....preventing fire. Please advise a rookie car builder that wants it done right even though I may never race it the car period due to many track closures in the Lone Star state. Thanks in advance as always. Texas Red