The Freezing Mist gun doesn't display when using the costume unlocks from reputation ground armors. I have tested this on Undine and Delta costumes and they both make the gun disappear. My toon still looks like he is holding the gun but nothing is there.
This is very disappointing since the armor would look awesome with that gun.
Comments
If you have an Eng Kit on the back when you equip the gun, the Eng Kit is removed.
They can't remove it when it's part of the armor - as would be the case with the Undine armor.
What backpack would need removed from this armour?
http://i236.photobucket.com/albums/ff233/khamseen_air/2014-12-05_00005_zps37177968.jpg~original
That's me 'holding' the Snowblower gun btw...