I spent some time countersinking the end caps and dimpling the skins. I read some other builders had some concerns over the material being too thin, but it seems they beefed up the thickness to allow for a good countersink.
Once that was done, I temporarily connected the elevator to the horizontal stabilizer with some bolts I had laying around and used some wood placed on the skins secured with some clamps. This ensures the elevator and horizontal stabilizer are perfectly aligned.
I made sure to only cleco one side at a time, per the instructions, and began riveting. The skin fit pretty well and didn't really have to ream out many holes. I flipped it over and repeated the process. The skin was a bit tighter on this side and took a few more clecos to ensure a good fit.
Nothing more satisfying than a handful of pulled rivet mandrels to finish off another piece!