It only took me till 2AM to get this working - here's the new 'layer' section that works with the arcgis vfr sectionals..
<layer name="us-vfr-sectionals" backend="texture">
<!-- Rendered tiles expire after about six months or 15,552,000 seconds -->
<texture name="us-vfr-sectionals_data" expire="15552000" >
<sourcedir format="JPG"> earth/us-vfr-sectionals </sourcedir>
<tileSize width="256" height="256" />
<storageLayout levelZeroColumns="1" levelZeroRows="1" maximumTileLevel="24" mode="Custom" />
<projection name="Mercator" />
<downloadUrl protocol="https" host="tiles.arcgis.com" path="/tiles/ssFJjBXIUyZDrSYZ/arcgis/rest/services/VFR_Sectional/MapServer/tile/{zoomLevel}/{y}/{x}" />
<downloadPolicy usage="Browse" maximumConnections="20" />
<downloadPolicy usage="Bulk" maximumConnections="4" />
</texture>
</layer>