Are you dead set on touring with a trailer? They can be a good idea if you need to carry a really oversized load (say you're touring with your kids and want to keep the weight off their bikes), but otherwise they're usually overkill. People buy them 'cuz they're neat and wind up taking fifteen pounds of trailer and twenty extra pounds of gear up every hill. Most serial bike tourists tour with panniers, not trailers.
If you're certain you need a trailer but want to minimize the resulting hassle, buy a Bob trailer. I see them often on Craigslist (people also buy them 'cuz they're neat but then never use them). They weigh a lot less than the others (mine is about ten pounds). You feel a lot less like you're dragging around something big and clumsy than you do with a two-wheeled trailer. They are really elegantly engineered and will be difficult to match or surpass in a one-off home build for overall functionality.
However, overall functionality is overrated, and building trailers is fun. If you're still moved to build one, then that's how it'll have to be!