Here are some photos of my all aluminum trailer:

http://picasaweb.google.com/Hulagon/VanagonTrailer

It has a Torflex axle with wheel spacers/adapters so that I can use
Vanagon wheels, and the track of the trailer matches the track of the van.

I can carry (4) bikes on the hinged lid.  The lid has hydraulic struts so
that it stays open with the bikes on.

The depth of the trailer box just lets me reach in all the way to the
bottom.

The length of the trailer box is sized so that when the trailer is
disconnected and the trailer and van are slid tight together (tongue is
slid under the van) both pieces will fit inside a 20' shipping container.

Kevin