One of our club members said he wished he had standardised on a transporter design, one that took into account the width and length of his ute tray, just to make loading and unloading easier. I haven't made a transporter yet, but I'm keeping that in mind, along with built in tie down points, e.g. eye bolts or similar. To me timber will be my choice, although I'm no woodworker.
Cockie