Thanks for clarifying for me, Salan! Though I don't think you can put AT guns in the empty emplacement. At least not 17 pounders.
Essentially, the emplacement becomes like a british version of the german bunker except you can also put a mortar inside, which is awesome. The only thing that needs to change is the ability to put more than one guy inside. So like it says it has a capacity of 12 but a single sniper fills it. Though having a sniper emplacement was pretty sweet!
I think it is an awesome way to do the emplacements!
I also like the idea of having spotters for artillery, though you can spam spotters and it is kind of ridiculous.
With the current way that garrison slots work, in order for an emplacement to be able to hold a weapon crew (at gun, mortar) or inf it can only have one squad in at a time. Fore more information read my How to: Add garrisonable building slots in the relic news armour, i wrote this how-to specifically for sturm.