No plans for one but mate had one knocking about before and it seemed pretty easy to knock up, it was like a big 8 where the front wheels dropped in, on a T shape to the hitch.
Found this one on google which I like better, but still looks copyable even if a bit posh with all the clamps and clips.
Edit, Darren, if you like I can get some detailed shots of a bike trailer and specs.
. Done a search for the indispension units they use but couldnt find any, as I was coming up with the bob standard ones for normal trailers, the units used on these seem to be lower from the hub itselft, so it would be closer to the ground for ease of access to the ramps
Ok will get some of the bike trailer.
Today I have been doing my trailer, and for the wheels/axle I am using what looks to be rigid rear beam axle off an old Ford, I think its a Fiesta maybe, not sure? But it is about a 3 inch tube with the backplates took off etc, and with reference to your point about getting something low enough, this tube drops below the hubs quite nicely which could make it suitable. You do mention suspension and this thing is obviously rigid, but just banging some ideas around.
I may be able to get some close up shots of a set of towing spectacles, mate of a mate got some and its just a matter of catching him, when I do I will take some anyway for future ref if too late.
They look kinda like some of the trailer ones i have seen but mounted the other way up.
On the far wheel in the piccy the hub appears to be higher than the base of the trailer - like it would be if you mounted a trailer one the other way up.
Cheers Darren, smart little thing