Flange - excellent project! Thanks for posting. (I hope you don't mind I fleshed out your thread title to make it more visible to people searching for this approach.)
The exisiting bolt holes made it fairly straightforward - lucky you.
That's a temptation I wouldn't have been able to resist! I have a lightweight (160 lbs / 73 kg) trailer that I sometimes use for light duty work. The car with the hitch is also not rated for towing... however, it's well past the warranty, so there's no disincentive for in me doing that.
We did consider having it made as a towbar, but figured that it was best to restrict it to a bike rack only, thus avoiding the temptation to tow a trailer in a moment of need.
View my fuel log 2014 Mirage base ES 1.2 manual: 54.0 mpg (US) ... 23.0 km/L ... 4.4 L/100 km ... 64.9 mpg (Imp)