Not a lot of work accomplished, but got over a mental block on finishing these sides.
Removed the sliding seat supports (front & rear) and trimmed the ends where they were preventing the side panel from sliding all the way in place.
Cleco'd the side in place (lots more had to be un-done!), then started adding the seat supports etc back in place.
I was a bit concerned yesterday when trying this because it wasn't clear whether the supporting L-angles (pre-made in this case affixed to the front or aft of the vertical side panel angles. It all makes sense now and is actually a bit easier the way that Zenith designed it.
Spent a lot of time clamping the side in place and ensuring the fuse bottom skin was level. I need a clamp my son borrowed, so stopped for the evening.