There is a very good description of this on page 15 or 16 of this thread. What I did was drill the struts as described in the manual, then slid the fairings onto the struts and bolted them on.
I then made sure the fairings were a good fit to both sides.
Once I was happy with the fit, I removed the struts and put a few dabs on 5-min epoxy / micro ballons into the fairings where they met the struts. Then bolted the struts back on with the fairings taped into place to make sure they had the right fit.
I didn't put a lot, just enough to lock them into place until the epoxy mix set.
Once I had done this, the rest was easy. I filled up the fairings in two or three portions until I was satisfied they wouldn't deform anymore. Each time bolted them back onto the plane and held in place with tape.
This sounds a lot more complicated than it is to do. It ended up with a nearly 100% fit