Drilled apart the practice airfoil and re-assembled it a couple of times to make sure I was comfortable back riveting the thin rudder skins, then dimpled stiffeners, skins, and installed stiffeners per print on 1 rudder skin. Ran out of time today, so I'll get the other side in a day or two.
I see people build all sorts of complicated dimpling and back riveting tables, but It seems like that's a lot of effort for something that isn't really used a ton, so for dimpling skins, I just set the DRDT on a old coffee table and built up a surface on each side of it with the cardboard box the skins came in. For a back rivet plate, I used a 6" by 18" chunk of 3/8" thick steel that I bought at the yard store for about $10, with a moving blanket folded up on either side of it to make everything level.