Step 2: Building the rough hull...
Since you're here on Instructables, I'm going to assume that you're already well-versed in taking things apart, so I'll skip the whole "how to strip down a weed trimmer" step...Let's just say that you're not going to throw anything away until your project is done, right?
I went to everyone's favorite Chinese retailer (WalMart) and bought the biggest box they carried, eyeballed the heck out of it (admittedly, I rarely used a tape measure for this particular project), and began cutting up my interior supports, using a framing square to keep the strips of an equal width.
I didn't really consult any plan on this...I just used a little common sense to figure out how much infrastructure I'd need to make my hull rigid once joined. I used extreme-surface masking tape to line up and join the interior girders to the bottom portion of the hull, and reenforced them with gorilla glue once everything was correctly aligned.
After the interior and bottom had a chance to set up, I used HVAC silicone to join the deck to the rest of the frame, and held it in place with more super-duper masking tape.
Since this is my virgin build, I have learned a few things that will help me on the next one. Consider these little tidbits as you continue.
Eventually, a motor is going to me attached to this thing...a pretty heavy, high-torque one. If I ever build another one like this, I'll fill the entire rear half of the hull with expanding foam, so I can bolt through the entire hull, instead of settling for a surface mounted plate.