If the cargo bed cover had been better sealed and stronger and the rear bulkhead more solid, then the explosion would have blown out the sides as those panels aren't fixed all that well as we've seen in the past. Instead it blew off the cover and went up, with concussion radiating out, and blew into the cabin area. Also, the choice of materials in the bomb has to be factored in -- fireworks and gasoline is nowhere near the bang you'd get from black powder + propane + ball bearings 1/2