Came across this random video, it's a build of a foam fishing boat, weighs under 30 lbs. Looks like some PMF application and a number of glue products. You can purchase full plans for $12 but from the video I would guess a handy person could figure it out. Looks like a very fun project and would go well riding on top of your tiny trailer!
[youtube]https://youtu.be/4sDubB0-REg[/youtube]
Building a boat is on my bucket list, if I didn't already have a few other major projects in flight or in queue I would start this weekend.