Maybe a good idea will be to plug in a BNC-to-RCA converter. It's cheap , small, and will protect the female BNC plug of the camera. And since it is fixed with the bayonet of the plug, it won't be easily detached by accident.

Mine didn't even make it out of the box with one. Must have gotten left on the factory floor in Japan.

Alexander,
the plug (or the cap) is not precious at all and certainly shouldn´t cause trauma. It really is a bit cosmetic. Broadcast cameras are being tossed around all the time with no caps on the ports and they never fail because of that. The connector is recessed and therefore quite safe. There won´t be any dirt going in the camera through it either.
The worst thing to do is to insert a dummy plug that sticks out, hitting such a thing might cause the circuit board or whatever the connector is soldered on to break. That would be a real problem. Let it be, should there be dirt in the connector; just clean it.