Ah my bad, you can find the rules for the fortress of redemption and the imperial bastion in the main rulebook as well as rules for using them.
Ah, that would be the problem, my friend has our only rulebook and I just have a working knowledge of it.
Anyway, I would say that the D-Cannons go in the Fortress, assuming they can fit. Because that is where the brunt of your firing power is, so why not go whole-hog. Also, it offers extra protection for them. I would imagine the character goes with them for the same reason the exarchs fire the Icarus Lascannons, if you roll sixes to wound, I'd imagine you could allocate wounds, even if it's a blast, based on what you've already said.