Welcome to Librarium Online!
I was just reading the rules on the use of a hellcannon, and it mentions that the Chaos Dwarfs "line up on either side of the hellcannon" as oppossed to in "front of it."
What does this mean?! Is this during combat or in general?! Does it really matter where you place the individual models for any type of cannon during play?!
Well generally, war machine crews are positioned behind or to the side of their machine. They only line up in front when an enemy unit charges the artillery piece. However, this is only for normal artillery, a Hellcannon is anything but normal, because I'm pretty sure that when enemies charge it, the cannon fights as well!
This is why the Chaos Dwarfs line up alongside the cannon, because it will fight the enemy as well as the dwarfs. So when not in combat you can just place the crew anywhere you want around the cannon, but in close combat, they line up with the cannon and fight the enemy that (foolishly) charged them.
"Peace, through superior firepower."
Believe it or not the hellcannon is a good flank protector. Most players will do their upmost to stay out of its firing arc. If it does get charged it can fight well in combat to boot.
Basically life sucks, there is only war and you're probably gonna get eaten by Tyranids, have fun.