Most trailers don't supply a qr spindle as fittings would vary from bike to bike
I have towed my model aircraft trailer 4ft x 2 ft x 1ft deep on a piece of angle iron behind the standard qr on my road bike and I fabricated a bracket for the trikes without problems which fitted to the mudguard / rack mounts on the rear triangle .
My trailer was built from 1.2mm 40x20 square tubing ( still in pink powder coat ) from a bed frame with a 5mm ply base , 300mm Upvc sides and ex-wheelchair qr wheels . if require a tarp can be used as a tilt to cover it if the weather gets bad or a wind/weather shield
The towbar was made from a redundant car trackrod end and a cranked tv aerial pole The two main rails bolted together and spaced with tube from the same bedframe and studding rather that weld up the frame
the interior I sprayed with matt black paint and the underneath sprayed with car body underseal to seal the ply from water ..
total cost was about £25 and a mornings work and a couple of hours scrounging bits .
I also use the trailer for collecting logs/ scrap timber for the wood burner behind the e-trike
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Fitting any ( ready built or home-made ) trailer to a bike / trike does require a little thought and a few ounces of common sense .
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regards emma