Casting Raw Byes To Struct In C++

I have been researching a bit about efficient methods of serialization and deserialization of objects in C++. I am writing for an embedded system so I am wondering if the following is valid?

static const uint8_t data[] = {0xAA, 0xBB, 0x10, 0b00000101, 0x0A, 0x00, 0xDE, 0xAD, 0xBE, 0xEF, 0x04, 0x00, 0x00, 0x11, 0x22, 0x33};

struct __attribute__((__packed__)) Message {
    uint8_t std[2];
    uint8_t id;
    union {
        struct {
            bool optionsReply : 1;
            bool optionsFoo : 1;
            bool optionsBar : 1;
        };

        uint8_t optionsU8;
    };

    uint16_t payloadLength;

    uint8_t payload[0];
};

struct __attribute__((__packed__)) TestMessage : public Message {
    uint8_t a0;
    uint8_t a1;
    uint8_t a2;
    uint8_t a3;

    uint16_t length;
    uint8_t data[0];
};

const Message* msg = reinterpret_cast<const Message*>(data);
const TestMessage* testMsg = static_cast<const TestMessage*>(msg);

I tested this with my compiler, and it looks like everything works as I would expect. My question is, because of zero length arrays that I am forcing to be larger at runtime via the associated length, is this the preferred/safest method of doing this?

Thanks