So just how many exploded trucks have you seen or heard about? You know, the one's with the "bomb" inside of them? Now the ones with the tank Outside of the cab have a higher incidence of incidents. If you want to move your tank outside of the cab, that's all well and good. But you're actually putting it closer to that speeding 18 wheeler that you can't get out of the way of. And if you want to keep it in the cab, well that's all well and good too. But don't think that you'll be more safe either way. If an accident gets to your in-cab fuel tank enough to cause an explosion, you were already in deep [censored] anyway.
If you're building one of these trucks to transport your daughter around the countryside, maybe a new car with airbags better suits your needs.