I wouldn’t worry KS.
Even a bolted down tank is gonna smash you to bits in a bad crash.
I had a crash in the ice back in 2016. The only crash I’ve ever had since driving at 17. My tank was 3/4 full and an old man in a saloon slid straight into my near side, the speed was about 50mph when you comobine both vehicles colliding. My tank was absolutely fine.
Van was repaired and back on the road 2 months later. His car was a write off.
I think you need to be involved in a really bad crash/sudden stop to succumb to the tank flying through the bulkhead.
My tanks have never been bolted in.