New Public Gist

main.cs

using System;
using ServiceStack;
using ServiceStack.Text;

public class GetPersonResponse
{
    public string FirstName { get;set; }
    public string LastName { get;set; }
    public int Age { get;set; }
    public string PostCode { get;set; }
}

public class Person
{
    public string FirstName { get;set; }
    public string LastName { get;set; }
    public int Age { get;set; }
}

var person = new Person {
    FirstName = "Bob",
    LastName = "Smith",
    Age = 40
};

var personResponse = new GetPersonResponse() { PostCode = "3000" }.PopulateWith(person);

personResponse.PrintDump();

packages.config

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="ServiceStack.Text" version="4.0.62" targetFramework="net45" />
  <package id="ServiceStack.Client" version="4.0.62" targetFramework="net45" />
  <package id="ServiceStack.Interfaces" version="4.0.62" targetFramework="net45" />
</packages>