To the OP
OP You could do this at 120Kg. No direct to towbar one will be suitable because of the bending moment on the hook.
Off the shelf Cate in Germany make a suitable rack for your needs. I photographed the swiss one on the Autoroute in France last year.
I tow with an Erde trailer which is very stable and always thought those motolug look a bit flexible. I cant see these sideways things are any advantage over the erde
I intend to go the Cate route but probably a diy one but thats just me. I have done the sums (for 250kg) and the only issue is really the rear axle load. I suspect at 120kg your ok but you would need to check.
Lots of advantages over a trailer if you want to get somewhere unconstrained by lower speed limits, my main reason for the change and easy of reversing etc
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