I've been playing around with the idea for a long time as well and finally
decided to get my feet wet (pun intended)
turns out that high frequency radio waves can't penetrate water.
like someone said, "Besides Lead, Water is one of the best containments
for radiation, so using a radio trigger under water is like farting against the wind
"
modern day subs use low frequency waves to penetrate deep for
radio communication... "the wave lengths are much bigger and wider thus
allowing for more errors"
got some nice suggestions from other people... like drilling a hole in the
bottom of the container so that the cable can go out (putting it at the
bottom will give it a "diving bell" affect) and seal the hole with silicon or
whatever waterproofing putty. the cable can then go directly to the
camera... or plug into the radio trigger which can float on the surface
while the strobe is positioned in the depths.