Positioning the holes was tricky. First I traced on the underside of the body around the hoop mouting bracket underneath, then "estimated" by drilling a small 3mm hole, then offset by 25mm (half the hoop thickness) and drilled another 3mm hole hopefully exactly in the middle. I was off by about 3mm, so I adjusted for that when drilling the 60mm hole and we're all good!
Drilling the second hole I marked out lines, using the rubber door mat you can see as a ruler - I just dropped the mat on the body and it follows the contour of the curved body perfectly. After marking parallel lines with the fist hole, a small pilot sanity-check hole, check it with a satay stick :-P and were off and running with another 60mm hole.
Sounds simple. It wasn't.
The final height of the hoop is not set, nor is the third leg in, as I need seats first before I can determine how high I want the hoops - for now the hoop is just sitting there.