So, I cut some 1.5"x1.5" wood strips that fit between the ribs. The strips are ripped with a 73 deg angle. That was empirically determined.
I pre-drilled holes to screw mount the strips and 3M 90 glued them to the walls.
They are screwed into the walls. Their height is set to just clear the roof rib metal.
These panels are mounted with a combination of VHB, 3m 90, and brads.
The first panel is up:
I would've said I was sure that the wood would fit like a glove, but as much as I need to give myself a rousing hand of applause, I could find no hands up there. So, although I would've said that if I could've said that, I couldn't say that, so I douldn't say that....(apologies to Ogden Nash)
OK, I now felt much better, so I installed the rest of the sides, except for the complex curve ones at the front. Those also have to fit around those foam blocks
For the front, I had to cut the pieces into a weird shape. This is the driver side piece:
In order to connect the front pieces, I added some tabs to the existing ceiling with TiteBond III.
The front pieces need to be "convinced" that they want to spend the rest of their existence in a contorted shape. The convincing took place overnight with 3m 90 and brads used as incentives. Here's our redheaded Irish convincer, Studs McSquash:
By the next morning, we, and the panel, found that Studs was quite convincing:
And so, excluding trim work (which will be done much later in the build), the ceiling and this chapter are done.