You realize that this is an emergency exit? Screwing bars across it is going in the opposite direction of what it is designed for. Even one bar and by the time you find a screw driver in a fire you are dead. And if you think you can pull it off if there is a fire then it won't be strong enough to stop someone then.
Also, why would someone climb up on top of a camper to try and break in??? They don't know if the hatch is big enough to fit through. You have windows lower down and a door that would be easier and faster.
If you are set on doing something then I would suggest making a hinged set of bars that can be locked in the closed position to stop an intruder. Then unlocked when you are in the camper and swung out of the way and attached in the open position to the ceiling. That way you won't be found dead looking for a way out.