So I've been working on this design for a while, but it's been hard to share because I'd need to do so in a screen capture. The reason being all the sepparate weapon pods are tethered to the main ship section as physics based elements.
The concept: I wanted to have a tank-like ship with large interchanging and upgrading weapons systems, but naturally in a game of this type you need to be able to dodge weapon fire. So the weapn pods float around the main ship creating a visual disconnect, Weapon pods aren't affected by enemy projectiles, and you only need to dodge with the main ship. | 
Nice.
Instead of making the secondary weapons invulnerable, you can make it so that if they are hit they also take damage, but have a seperate healthbar. They would get hit more often, which punishes unskilled gameplay, but allows a skilled player to just bust through the enemies with hard hitting secondary weapons.
Just a random suggestion, I think it would be a unique game mechanic.