Why isn't Autoblog featuring the image from the RSS enclosure tag?

I am exploring Autoblog to aggregate from classified content from Craigslist.
Sample feed

In the RSS items include a featured image like so..
<enc:enclosure resource="https://images.craigslist.org/00M0M_lkRuZI4OS7H_300x300.jpg" type="image/jpeg"/>
Under Auto Blog > All Feeds > Edit Feed > Featured Image Importing
I have tried to use all three settings to null effect.
- Use enclosure tag of a feed item
- Find the first image within content of a feed item
- Find the last image within content of a feed item
None of these three appear to grab the image from the item tag and make it into the post featured image. I have also tried the "force feed" option and that doesn't appear to get Auto Bot to process the featured image either. What am I missing?