The tail spring mount is another part where the Van's instructions are fairly vague. I spent a lot of time studying the plans and researching on line.
I started by cutting out a section of the skin where the tail spring extends out. This process took a while to get an exact fit.
I also enlarged a hole to allow clearance for the tail spring nut.
The rest of the time was spent measuring the tail spring mount, checking alignment and coming up with a plan to drill holes for the bolts that secure the mount.