As long as they are not nearly as powerful as Gunboat missles, i think its a good idea, it would give Transports at least some defence vs. Bombers.
With a missle mount, flying in Convoys would make sence over night. A single Train, even with an escort fighter, has no survival chance vs. a bomber, neither have 3 or 4 Trains flying together. But if all could mount one, small missle turret, a lone Bomber would die to them.
And if there are more than one pirates, the transports at least have a fighting chance.
Some Trains might get trough.
