Other rebel builders on the builder list reported on cracks at the elevator outboard rib. After having test fitted the elevator tip with a relatively heavy counterweight, it is clear that there will be some twisting force at the elevator end, which may over time lead to cracks in this area.
As proposed by the experienced builders I decided to install reinforcements at both elevators: 0.025 sheet parts to reinforce the skin at the end and shortened elevator ribs riveted to the outboard rib.
Worked pretty straightforward. Nevertheless a strange feeling doing precautionary repairs before the plane has even flown once.