Wow @Eric, this is a nice scratchbuild conversion. what type are the guns?
I would object to the tactical concept of Your train though, if You don't mind.
So over the various uses of armoured trains, the tactical use established types into two basic concepts.
The first is the combat train with basically two types, light and heavy, by manufacture of armour and often including improvisations. Armament used to be light field guns or mortars up to 75-100mm and a lot of machineguns.
The second concept is the support train, with heavier and longer range artillery, and usually only defensive purpose support weapons. As usual for artillery units, AA cover is a good idea. Armour would here be of the lighter type, because these would not be supposed to purposefully operate under enemy fire. Reserve elements like infantry and cavalry cars could be included.
Railway artillery is not covered in this breakup being of a different purpose.
Now Your railcar has the center armoured cabin with firing slits (combat role), while it has large calibre artillery (support role) that are completely without cover. This is a bit of a contradiction.
I would suggest to abandon the firing slits and make the center compartment a command and ammo station, maybe by adding a rangefinder? Plus adding fold-down service platforms with side stabilizers to the main guns that can double as light armour during transport.
Of course VBCW offers a certain flexibility with history, plus You can do whatever the hell You want with Your construction. And You certainly don't need my uninvited advice
I just thought I'd offer the bit of research and experience I gathered with my own armoured train projects if You like to be entertained by it