I bought four double-lasers from Puppetswar for this exact purpose. Whilst I could have made my own (and I did try), by going down this path I am able to keep all eight guns identical.
The only problem I have is that they look a little small. The guns' calibre and length are about right, but because they are tightly packed the whole weapon system looks dinky. So, to combat this, I’m adding armour…
And the first on the list will be a Hunter-killer Missile, since Chaos Space Marine players generally don’t get to have fun with those infinite range rockets. I wanted to choose a sleek and slim line missile for the basis of this option, so I’m going for one from the current Chimera kit. It is ideal, but I want to inject a bit of ‘chaos’ to it. I’ll grind out a chunk from the nose cone, and with greenstuff, sculpt a daemonic eye and teeth, to make a cool-looking daemon-sight guidance system…very chaos.
I think after this first option I will start painting the monster. It will be an educational experiment, as I plan to do my first-ever salt weathering, and first ever OSL with an airbrush. All-in-all it should be a fun conclusion to this project.