I cut the ends of the boards first to the angle they need to be......
I lay out the pins square to the angled end, and cut those. Once the pins are all nice and cleaned up, I lay out for the tails.
On that tool tote all four sides splay out. I'd have to check for the exact angle...protractor says it is 20 degrees. So, I just cut all the ends at 20 degrees. The dovetails turn out to be square to each other..
Attachment 357085
I was trying to build a tote like Underhill made.....didn't care for the nailed corners. Was easier to do all the sides splayed out. I made mine to be able to hold a full sized handsaw. Dovetails are 1/2" through style though some of the spacing got altered, due to knots in the way....
Attachment 357086
That is a D-23, 26" long crosscut saw.
Attachment 357087
YMMV. Not really "Rocket Science" nor "Brain Surgery"......