This is something that I was inspired to make by the current Modding Contest, but by no means do I intend to submit it. (unless something makes the end product truly amazing)

Its simply a bunker with a Cyber Elf as a brain, two REALLY weird turrets, and fail placeholder sprites.

I'd like some suggestions to make this better, since I plan to eventually put it into my main project.

This is a really good start, but there are a few changes that could be made to improve it.
First and foremost - sprites. Improving the sprites of the bunker itself to look more vanilla-like (cough cut apart the vanilla bunker modules cough) would make it a lot more appealing, as well as polishing the current turrets.
Secondly, the turrets themselves could do with some tweaking. They currently are extremely large and unwieldy at closer range, and are also very weak. They do not do much damage and are very susceptible to instantly disappearing. Being even bumped in to by the engine of a dropship causes them to cease to exist. A bit of lua could prevent your guns from swiveling at such wide angles and stop them from facing inward at your brain.
Third, I would suggest scaling the entire bunker down, and making it more willing to be included in existing bunker designs. This means creating entrances for other bunker pieces to be hooked up, and vanilla-fying the whole mess to be more coherent.
Hope this helps!

Thanks so much for the advice.
I knew I'd need some better sprites for this, I mean, really the current bunker sprites are simply placeholders. I'll be sure to change the turret sprites as well. The main thing about the turrets is that I didn't realize that a very loosely limited line of explosives "do not do much damage." I was looking into some lua that might limit the angle properly, and I found a few things, so that will come soon. I thought I had set the GibImpulseLimit and the GibWoundLimit high enough that they'd be durable enough to withstand some pretty crazy stuff. Well, back to GIMP and Notepad++ I go!

If you'd like, I could throw together a sprite for a turret gun.
There's a snippet of .lua for the Nailer Turret in the Experimental Dummy Vehicles mod that does the trick. I'd suggest asking for permission, though.
If you need a powerful explosive weapon, I've got something I can send you.
I'd suggest not only doing that (I'd suggest at least 1280000 GibImpulseLimit), but also increasing the joint strength of the gun itself to around 12800.

Sure, I could always use a better sprite. Are the explosives simply not working on your end? Because I'm surprised that you don't think that it does enough damage already, since it easily rapes almost anything in its way. I had completely forgotten JointStrength I'll work on that too

Just from what I saw, it fired Revolver Cannon rounds with the occasional Pistol sound effect. The rounds fired by the Revolver Cannon are okay against single infantry targets, but they tend to bounce off armor like Dreadnoughts and Dropships, or, at least, from what I saw in my tests with your turrets. The explosions from the shots are rather weak, and could do to be more flashy and powerful.

The whole point to this weapon is not the initial shot, but the trail of explosives that it leaves behind. Would you please post a screen shot/gif of what happens when you fire it??

Won't bother uploading a screenshot, it's just a projectile that doesn't even seem to do damage.

I fixed that. I referenced an earlier version of this mod.