That'll definitely be a safer place for it but still it could come lose during an accident & start flying around, so I'd still strap it in somehow imo.
Reason I say this is because I speak from personal experience of rolling one of my old cars at high speed down hill when I was a lot younger. I had a 1.5kg fire extinguisher which during the crash broke free of it's mountings but luckily it didn't hit me.
Also had an MDF stealth parcel shelf with 2 kenwood 7"x10's in it come flying at me, ...again, luckily it didn't hit me.