No problem. That's just the fill neck, as the actual tank is under the car...right next to the exhaust pipe. Also, the fuel tank itself likely has an electric fuel pump SUBMERGED in or hanging just above the gasoline. The key, as usual, is in proper design.
Make sure to properly secure any box you build to the trunk floor...50 lbs. sliding around in your trunk with every turn is much more of a concern than a gas tank explosion.
Also...you live in The Colony? I'm there quite frequently, as I have family there. Have you checked out the North Texas Meet thread (linked in my sig below)?