I haven't experimented with the feasibility of this type of ship, of course, but here's the idea:
Early on, the enemy only gets Tiny & Small hulls. So, put a bunch of weapons on cargo ships. You can only take one hit, so to counter that you cram a bunch of defense on the ship with all that extra space, like 2 armors, 2 shields, and 2 ecms. Later, you can convert them into transports or decommission them.
What do you think?