Check out this guy's DIY longtail:
Although it won't allow for the same deck height over the back wheel, it might be more sturdy than an xtracycle. It should even be possible to replace the top struts with a long shock absorber to make a suspension longtail.
The rest of the pictures in full definition:
http://www.flickr.com/photos/7675758@N03/sets/72157611969221412/
Although it won't allow for the same deck height over the back wheel, it might be more sturdy than an xtracycle. It should even be possible to replace the top struts with a long shock absorber to make a suspension longtail.
The rest of the pictures in full definition:
http://www.flickr.com/photos/7675758@N03/sets/72157611969221412/