So close! Rather than using %addr(Reserved) try %addr(RcvVar).
But note that ptrMsgTxt is not pointing directly to MsgTxt. It is pointing to another structure which contains:
Offset to next message entry
Message enqueue date and time
To find the message text you will need to increment ptrMsgTxt (or its equivalent) by the bytes allocated for the first three fields within this sub structure.