Hello again. I've been getting some advice from my technically-minded friend, and have come up with an alternative frame design. The pieces are now cut - though they do need to be trimmed a bit. I'll try to weld them tomorrow, if I manage it.

Once it is welded as shown, I am going to cut out a ~10cm section from the middle of each of the short ends (and the cross braces), then shift the resulting two long halves back together, thus making the whole thing about 40-45cm wide. This is so that it will be no wider than my handlebars. I have drop handlebars on my bike, and they're fairly narrow. The frame as it is now is already narrower than handlebars on many hybrid/commuter bikes, but I want to be able to go exactly where I could go before, on my current bike (since I don't know when I'll be employing new bikes or anything).

Plus, a single-wheel trailer needs to be pretty narrow, I imagine, for stability.

Seeing this lovely big trailer frame is tempting me to make a two-wheeler instead, though. The one-wheeler will be such trouble to get right!

My idea at the moment is to paint the frame green, and then have a black fabric linining on the inside of the cage, so that the green tubing is visible from the outside. I reckon it would look pretty cool.