title: Three.js Multiple UV maps on a single object
body: <p>I am trying to figure out how to use two different textures on the front and back of a box. 
  Whenever I scale my box (ExtrudeGeometry), the UV maps do not seem to update. Therefore I am defining my own UV maps for the front and back of the box. </p>
  
  <p>To define the front UV map I use:</p>
  
  <pre><code>geometry.faceVertexUvs[0]
  </code></pre>
  
  <p>which works accordingly. <br>
  For the back UV map I use:</p>
  
  <pre><code>geometry.faceVertexUvs[1];
  </code></pre>
  
  <p>However I am not able to access this 'second' layer UV map.</p>
  
  <p>So my question is: </p>
  
  <ol>
  <li>Is it possible to update the UV maps accordingly to the scale of the object? </li>
  <li>Is it possible to access a 'second' layer UV map within a material?</li>
  </ol>
  
  <p>I created an example here: <a href="https://jsfiddle.net/gpxfatd4/5/" rel="nofollow noreferrer">jsfiddle</a>.</p>
  
  <p>I created three different boxes, with 3 different scales. From left to right: 0.01 x 2.97 x 2.1, 0.01 x 1 x 1 and 0.01 x 0.297 x 0.21. On the most left box, the textures are only covering a small portion of the box. The middle box has correct texturing. The right box has the updated uv map (otherwise only a small portion of the texture would show up). <br>
  (I am required to use the small scale on the box!)</p>
  
  <p>I hope someone can help me out!</p>
  
  <p>Three.js 84</p>