Don't all strobes fire when you short the ground and fire pins together?
If so, you could rig a momentary contact switch to do that. (making it waterproof and pressure proof is the tricky part.)
Use:
-a sync cord connector to attach to the strobe
-a water-tight, pressure proof box to house the switch
-an o-ring sealed button to activate the momentary contact switch (or if you wanted to get fancy, a cam activated reed switch would probably be easier to activate [very little pressure need to pull trigger])
-an o-ring sealed cord penetration in to the box
-pistol grip would be ideal (assuming you're hand carrying the strobe from location to location)
Take Care,
ChrisS