Bolts to make nightlatch more secure?

[rarara]

I have a storm door which has a nightlatch and a rim latch - not the strongest considering the size and structure of the door, since the things are only as strong as a few screws going into the wood.

I was hoping to find something like small coach bolts that could go through the full thickness of the door in place of the screws, but it looks like they are not made in such a small dimeter (would it need to be say M4?).

Can anyone suggest something suitable to beef-up the door?

 

[rarara]

Looks like these size of bolts are not available, but what I did find are various items like London Bars etc which can be fitted to say the back edge of a door and form around a lock or keep to provide extra oomph.