well you seldom hear of a ferry having a near miss,its either nothing,or its a herald job.
if you hit the water in the irish sea then lifejacket or not your probably going to die within 10 mins of exposure and theres not exactly going to be a queue of rescuers.
on any big ferry ive been on,then if your in a cabin,and as a truckie,itl most likely be an inside on,then if theres any major grief youl will be drowned like a rat in a trap.
you can always go up out the locked deck doors in an emergency,its just you cant get back down from the passenger deck.
if im not going up for grub ( and thats dependent on the boat) then il cab it every time for a good sleep in my own space.
you dont get disturbed,and you dont get tannoyed to death or wakened early.
personal choice of course,but ive always cabbed it to suit my whim on any ferry ive been on.