Fair warning! This is going to be a biggie Instructable. Fair warning! I suggest you read the WHOLE THING before you start building. You may also want to obtain some more detailed plans that include more detailed drawings and dimensions.
Over the past year I've built a 'teardrop travel trailer.' It's been an adventure for sure. It's very much been worth it. I aim to introduce you to the idea of a teardrop trailer and the steps involved in building one. You WILL need more info to complete a build. I strongly recommend the forum below.
I stumbled across this idea because my wife and I were thinking about buying an old airstream trailer to fix up. Then I stumbled across this web forum: http://www.mikenchell.com/forums/
It turns out that these teardrop (named for their shape) travel trailers were once very common. Especially after WWII in the states. Often built of materials at hand and ranged from minimal to elaborate. Check out this link here: http://www.mikenchell.com/VintagePlans/vintageplans.html.
Well I was hooked. I considered various designs and what I wanted in a trailer. You can track down a TON of resources through that forum above, as well as many gracious and helpful and wonderful people. There are a variety of FREE plans and a few at modest cost. Note: be wary buying plans on Ebay. Evidently, there is a fellow who pops up selling the free plans available from the above forum.
I decided to build a 'Cubbie' type trailer, based on plans from a company called Kuffle Creek. http://www.kuffelcreek.com/ But with LOTS of modifications. You must understand that no two trailers are remotely alike! One reason I picked these Cubbie plans is that there was NO WELDING. Certainly there are designs where you can weld your own trailer to spec, but mine started out with a bolt-together utility trailer from Harbor Freight. So without further ado....
P.S. At the time of initial publication (July 2011) I've got the trailer roadworthy, but it's by no means finished. As I complete further finish work I'd further steps. Please feel free to ask Qs in the comments and I'll respond as best I can.