You can quite safely use personal radios in the back, as many troops do.
Two snags there. One, you have to have been issued a PRR in the first place which the MERTs aren't (as mentioned in the report), and even if you do have one, all your conversation will still be drowned in the whine of two engines, five transmissions and the navigator.
You will notice that some of the team are wearing flying helmets so could plug into the intercom system
....which is also used by the crew to try and operate the aircraft. A crowded intercom is as big a pain as a crowded aircraft.
We have an OCF not an OCU. As far as I am aware, they don't
Get aware then. Yes, they (the instructors) do.