JD-EE
forget about the HF, when I had the dubious pleasure of using it one could go several hours without getting through.
Crossing the ITCZ especially in the middle of the night the important bit was finding our way through the cells.
Secondary was transmitting on VHF to let the other aircraft know where we were - same as over Africa and Asia.
We had the luxury of a double crew and occasionally we had the second captain watching as we transited the active zone. There was never ever an occasion when the working skipper was off the flight deck during the critical phase.