Really great to see the tunnel photos Trooper, as I want to use the tunnel next time. From personal experience last summer Ferries now scare me.
I haven't used Poole - St. Malo but I used Portsmouth - St. Malo (Brittany Ferries) last July and was rewarded with a dent in my caravan wall. I was packed so close to someone else on the car deck that when they opened their car door it hit my brand new van's paintwork and dented it.
Brittany Ferries were pretty casual when I complained, so never again.