How to handle Vec<Vec<u8>>

Hi,
i have a message to send in the form of:

type PubKey = Vec<u8>;

#[derive(Serialize, Deserialize, Debug)]
#[serde(tag="kind")]
pub enum Envelope<T> {
    Greeting {
        #[serde(with="serde_bytes")]
        id: PubKey,
        #[serde(with="serde_bytes")]
        shared: PubKey,
        thin: bool
    },
    AllKnown { 
        all_known: Vec<PubKey>
    },
}

As you can see, PubKey is only a Vec<u8>, what is the most idiomatic way to pack this. I do not want to put the Vec<u8> in a struct to use serde_bytes.
Is there something i am missing?
It would be really neat to annotated all_known just with #[serde(with="serde_bytes")].
It seems a pretty common problem to be to have an array of byte arrays.

Start from the serde_bytes annotations and the Vec field shown in the issue. Review the repository’s existing handling and tests for byte vectors, then determine the intended API for collections of byte arrays. Done means the requested representation is supported or the limitation is documented with coverage for the chosen behavior.