I think a positive pressure (if possible) system for the driver's area of confined bodies might help.
Actually you would only need a couple inches of water of positive pressure to prevent fire coming in, and for a smoke check.
You can run down to a theater and performing arts supply store in most major cities and rent a smoke generator for a day. Put it in the cockpit and turn it on and button everything up and watch to see where the smoke comes out. If you have the required drivers air vents all you would need to do is tape a hose to them from a boat bilge blower to apply a few inches of water pressure to the smoke filled cockpit and any openings will turn into old faithful geysers of smoke.
Some tuners use that sort of smoke system to find intake manifold leaks too, so it has other uses too!
I think a double layer fire wall would be good to consider in areas where you have penetrations like cabling and peddles. Put a second layer spaced a 1/2 inch or so from the fire wall proper so the fire needs to work its way through two gaps not one. That would significantly increase your burn time safety for very little cost.
Another idea would be intentional burn through ports some place in the engine compartment where the structure was intentionally designed so it would quickly burn through and provide a planned fire/smoke exit point. A small panel of low melting point styrene plastic designed to burn through quickly comes to mind, or a thin lead sheet or other low melting point material.
Larry