I know I have seen a lot of threads on riveting the trailing edge and thought I would share how I decided to rivet the rudder trailing edge which turned out with zero twist (as far as I can measure with a digital level) and very little pillowing.
1. Before rudder assembly attach a 90 degree piece of aluminum angle to the side of a workbench (long enough to fit the entire trailing edge and use shims with a digital level to ensure it remains straight across the bench.
2. Match drill holes from one of the skins into the aluminum angle that you just installed in step 1
3. Complete all other steps up to the double sided tape on the trailing edge.
4. Tape the trailing edge together per the instructions and cleco the taped edge to the aluminum angle. Allow it to sit overnight.
5. Remove the cleco's and replace the aluminum angle with steel angle of appropriate thickness for back riveting. (shim the steel just like the aluminum to get a flat surface).
6. Use rubber clamps to secure the end of the trailing edge to the steel angle and back rivet the trailing edge IAW the instructions provided by Van's.
Their were a lot of steps such as priming, riveting the skeleton and so on that I left out as I solely focused on the trailing edge here, but this worked out really well as you can see in the photo. The rudder trim tab that I fabricated got in the way of viewing the entire edge, but it has zero twist all the way to the end as far as I can see and measure.
Hope this helps someone who may be approaching this step.