Well, I'm glad to be convincing.
>Though I still can't picture… there not being some sort of ammo feeding, weight or aiming issue with an autocannon
You'd have to either do some real whizzbang kerjiggering to make it fit in an existing turret without extensive refit or draw it up as part of a new turret project, definitely. I think the biggest possible problem is that you're putting a bunch of 20-30mm firecrackers into the fighting compartment, which- unless you're a post-Soviet- supposed to be as empty of non-blast paneled ammo as possible. It would not be pleasant for a belt of this stuff to go off from enemy fire, so either the feed needs to be real robust, or you have to use magazines or clips that can go in a blast panel magazine.
>I think with external racks you're just asking for maintenance issues
Bolt them on firmly at multiple points with armor material class plugs on an extended side platform, or put them in a pluggable turret ring on the roof. Make sure the connector wire has some spaced armor shielding so it isn't cut by shrapnel. Make sure you've got lotsa wire at the depots for tank resupply. Make any hydraulic/mechanical elements of your missile zit turret or platform swingarm are dirt simple and sturdy, with nothing foulably fancy. No problem there.
>and unwanted detonations.
That's more likely. But if the enemy is trying to sink shots on your missile modules from a flank (if they're in your front they can be reasonably assumed to be good as dead) they're either dumb insurgents who either miss or won't get past the reasonably light & cheap fiddy-proof sharp angled RHA box, like a wee Patriot launcher set diagonal, that they may or may not be contained in and have now announced their position by trying to take you on like you were a Metal Gear boss fight. Or they're really dumb tankmen who don't understand that if blast panels can redirect an entire magazine explosion out of a tank, then a shaped charge or frag missile on a stick pointed forward from the tank will probably not do sPost too long. Click here to view the full text.