Coroplast
Here's a blog with a series of at least 11 very well documented builds
Video of Ken Stadden's fabulous build around an ICE Q (QNT?) that he modified.
Other
- John Tetz's Foamshell Velomobile
- John Tetz's Zotefoam Manual - great info on creating a plug!
- Rick Wianecki's Velomobile
- Dan Kildea's Velomobile (composite) on BROL
- and Dan's blog
- The Tinker's Workshop (info about his velomobile project seems to be concentrated in Sept 2103 entries, but can also be found after that for the next half year or so.)