Living Car Free - question about large cargo trailers

I am looking into buying a large cargo trailer for my bike. Since I can't drive, I want to maximize my bike's carrying capacity and hence, minimize the frequency at which I need to solicit help from some truck-owner. The largest I could find was about 8ft. x 1.5ft from Bikes At Work. In fact, all of the trailers I found were 2ft. wide or narrower. Is there a practical reason for this? Is there any reason why a 3ft. or 4ft. wide trailer wouldn't work?

I was also looking into building my own trailer. Does anyone know how to predict the weight capacity for a trailer design? I would think the most important factor is the type of wheels. Also, if I build my own trailer, what kind of hardware do I need in order to mount the wheels? Since I don't have the knowledge or equipment necessary for welding, is there a way to build a frame with bolts rather than welding?

If you can answer any of these questions, thank you. Eli

The main reason that bike trailers are narrow is that the bike "profile"
is narrow. To have any wider object behind the bike is to invite a crash
when the object snags on a something after the bike passes.

Bolted assemblies are never as strong as welded assemblies. While
you can bolt a trailer frame together it will require that you check the
torque on the bolts before each and every heavy load to avoid failure.

Wheels sould be no larger that 20" for strength as larger wheels will flex
to much under a heavy load.

Then there is the bike itself.......
A bike for heavy loads will require a robust drive train and steel frame to
take the loading and side torque from the trailer. This bike must also have
a majority of it's gears to be very low in range to move the load. No speeding
here, mate. The brakes must also be up to stopping the whole bike, trailer
loaded, and all.

Then there is you.........the bikes engine.
The basic question here is.....How "robust" are you??

Center for Appropriate Transport -PDF-
http://www.catoregon.org/hpm/HPM2005.pdf

The footprint or dimensions are designed to fit into a bike lane. Some of the bikes carry 6-700 lbs!

One relatively easy do-it-yourself solution would be something like the do-it-yourself cargo trailer from Wike (http://www.wicycle.com/trailer.htm).

Now one other suggestion I would make : if you make or buy a large trailer, think of also buying a smaller one. A trailer like the Burley Nomad is large enough to carry 1-2 weeks of groceries, yet it is light enough that you won't feel it when it's empty.