Battle Dress and Vacc Suit skill
Battle Dress skill, in my opinion, is a combination of vacc suit and also all the fancy heads up, sensors, weapons, powered augmentations, and other features battledress has that a vacc suit wouldn't.
My House Rule:
- Battle Dress skill can be substituted for Vacc Suit skill but Vacc Suit skill can not be used to substitute for the Battle Dress skill; except for vacc suit like features of the Battle Dress.