I glued five sides of the first speaker and the braces in, today. The small clamping jigs I made worked out well. I had two snafu's: the center brace was too long, I took the measurement of the length from the wrong panel, I guess. A saw fixed that. Also, I nearly premanently glued in the bottom hatch. Luckily, I remembered that I had spread glue on the center brace where it meets the bottom panel. I unscrewed the hatch and set it aside.
I filled all the joints where the panels meet with PL400 construction adhesive. No air leaks in this cab.
Tomorrow, I will get some stuffing in the cab and glue on the front.

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