Sorry to hear this.
I have a safe mounted under my front seat. It's hardly visible from outside the car but I draped a small towel over it to make it less conspicuous. Technically a gun safe but it's suitable for wallet, keys, etc. I recognize that locks, and safes, only keep out honest people but also recognize that most burglars don't want to spend more than a few minutes so they don't get caught. It's unlikely one could get in my safe in a few minutes. There are larger options available.
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EDIT: I really should have vacuumed my car before taking photos.