Head: Heat-Viper commemorative series
Torso and helmet: Payload V. 2
Arms, crotch and upper legs: Cobra Commander (Fred VII armor)
Feet: One each of Tomax and Xamot
Weapon: JvC Wet-suit (I think...)
Backpack: CORPS
Depth-Vipers are not a unique brand of Cobra soldiers; they're ordinary Eels with training for deep sea diving. Sometimes when Cobra administrates operations at the very deepest bottoms of the sea, the Eels put on a different wet-suit adapted for the higher pressures and icy cold environments of the ocean and then they go down to tend to their orders without objections.
The one problem the Depth-Vipers are faced with is that they need to remain on the bottom for days during the whole operation, as the extreme depths requires a mixture of helium-based air in order to survive - and once the divers are finally brought up, they have to spend another several days in a pressure-chamber to avoid falling victim to caisson disease. After that they return to their ordinary duties as Cobra frog-men.
What must be remembered is that just because they sometimes spend time at the deepest bottoms of the sea, you should still not underestimate them: they are still the same devious and ruthless divers of Cobra, no matter what depths you encounter them in!