EDIT 8/5/2020: the AK41H rivets identified below won’t work. See my later post regarding the side skin install.
Among other things, this past weekend I came up with a tool to dimple the holes where I intend to install flush rivets. I received my supply of AK41H countersunk rivets from SW Anderson Co, and performed some tests on a scrap piece to ensure I would be happy with the results; the pictures are below. Happy with the results, I turned to the aircraft to start looking at which holes need to be dimpled, and I quickly realized I didn’t have a way to dimple the channels that fit behind the side skin – due to the U-shape of the channel, the dimple die I bought from Aircraft Spruce that uses a nail and a pull riveter doesn’t work, because the channel blocks access for a nail. I don’t have a squeezer and dimple die, nor did I want to invest in a squeezer at this point. I’m also not sure it will work, the standard dimple dies are fairly big, so it may not fit either. So, I came up with my own solution: a modified Pop dimple die temporarily attached to a set of locking pliers. Admittedly, this is not completely my own idea; such devices exist, but not one that will fit into a tight space, nor one the proper die for a 120 deg dimple.