Tips for paneling a vaulted ceiling that nobody talks about

I did a similar run of boards over my garage workshop last spring, knotty pine tongue and groove, and my experiance matched yours on the prefinishing point. I used water based poly on the boards flat on sawhorses over two weekends, and even then I had to touch up a couple of spots where the joints opened slightly once the boards acclimated. Skipping that step overhead would have been brutal. One difference for me was the lifting. I borrowed a pair of scaffolds from my brother in law instead of renting a lift, and for a sloped ceiling they let me stage a whole stack of boards and work across a wider section without climbing up and down constantly. They were awkward to move between bays but worth it. I still had a friend spot me for the pieces right at the peak, and even with two of us the long 14 footers were awkward til we started cutting them to land on every other rafter.

On the chalk line thing, I'd add that I snapped my layout line from a laser level instead of measuring down from each rafter, since my ridge had drifted a couple inches over the length of the room. The line kept my first row honest even though the rafters themselves were not perfectly parallel. Shimming a few boards sideways to keep the courses tight worked fine and the trim hides all of it.

Not sold on the scaffolds for this job honestly. Mine sit dead level and my ceiling runs at a 10 pitch, so anywhere near the peak I was reaching overhead at a bad angle and leaning off the platform edge to hit the top courses. A lift tilts to match the slope so the panel comes in flat against the boards instead of above them. I rented one with the slope cradle and it held the board at the angle while I tacked the bottom edge, then let go. Did the whole ridge row solo that way. Maybe scaffolds win on a flatter ceiling but for a peak I don't see it.

I'm a long time reader, first time posting here, so hope this is the right place. We did a flat section over our dining room last fall, no lift needed obviously, but the wavy old joists were the enemy for me. I had to scribe the first row along a string and plane down a couple of spots so the joints would close up. My question is about acclimating, did you all bring the boards into the heated space weeks ahead? Mine sat in the room for three weeks and I still watched gaps open and close on the box.