Cool, thanks. ;-)
Very flexible.
I thought of that but unfortunately, unless the bracket can be clipped into the trailer frame to prevent the bracket rotating on the top frame, I'm not sure it will do what we would like? (The 'U' section could be made strong enough to maintain a tight fit on the frame but
1) the frame itself is quite light and isn't bolted hard to the (plastic) front panel at the top so would probably twist when any torsional load was put on it and 2) The (thin) metal top frame goes up the outside (about 25mm), over the top (our 22mm) but only back down on the inside about 15mm, so not really enough for any bracket to rest on (especially with that length of lever))?More importantly (re 3d printing), unless you provide a disposable 'raft' under the bracket whilst being printed, I'm not sure it would print with that angle and partly the reason I had the dowel level with the top face of the bracket, thinking it would have to be printed upside down. You could print the angle as long as it was carried though into the top plane of the bracket. That also raises the question of being able to print the socket. You could do that if printing it with a removable support plug or print it with the open end facing upwards as long as the rest of the bracket was designed differently. Bottom line, you can't print big or instant overhangs without including a support raft or leg etc.
Back on the usage ... If we tried to make the poles slightly overlong (thinking plastic conduit here) and if the brackets were designed the other way round (with the open 'U' facing outwards and could be a rounded U and shorter so printable)) and sprung into the trailer, we 'might' be able to maintain a form of 'hump back'.
I think 'flat' or even a very slight dish to any support solution will be ok (and simple) as currently there are just a couple of nylon straps stretched over the top front_to_back under the cover and they allow the water to shed ok.
My idea for having the dowel level with the top edge of the bracket was that if it went inside a tube of some sort, the tube would be raised above the thickness of the bracket (by the wall thickness of the tube) and the tube could be notched over the top of the bracket to remove some of the stress on the dowel itself and stop the brackets rotating with respect to each other (even if only a push fit on the poles). I think the dowels (or socket etc) only need to be long enough to stay on the pole and generate enough support between bracket and pole. Too short and the bracket could fall off easily then being handled (if not attached or an interference fit) and not provide much support and too long would just be a waste of time and plastic. ;-)
Just thinking out loud etc)
Cheers, T i m
p.s. If once I can give you an actual dimension for the dowel (when I get some tube) could you leave the item on the base with the 'U' facing upwards please as you know what trouble I had rotating the last item! ;-(