Just a little bit of work today making my Genswick Autocannon teams. I utilized SM Landspeeder Assault cannons for a Gatling-gun look. I recommend, when ever working with assault cannons for anything, using a pin vice to drill out all the barrels. It will make it look so much cooler.
These will be the only non-wheeled heavy weapons, as my mortars and lascannons will be based off Ork Kannons and Zzap Guns (plus I couldn't reasonably find Empire Cannon chassis for these).
I particularly like the guy dousing water onto the barrel of one of the guns to cool it down.