I had a 650 IBC in an Expert van.
Crashed at about 35-40mph.
Frame bent to about 45º but was bolted through the floor and box section underneath (what we used to call the chassis?)
Plastic liner inside-stayed intact.
Some water sloshed out as the lid flew off.
The fella i was working for at the time removed the tank and frame and left it outside the yard as a reminder for me every morning until I left him.
I never crashed his van again
He did put me a new IBC back in to get out to work again.
I never had issue with it. I posted about it early on in my CIU life.
Far as I know, at the time, no-one else had crashed with an IBC in so no real evidence to go on.