Don't have that jig, but it seems to me that if you edge glue up the 8 and 10 inch boards, you will have an 18 inch wide boad, which when cut to length, can simply be rotated as you assemble the case. So I'd glue up the boards, then cut and create the joint you're going to use on the corners.
This is the kind of case that probably should have at least box joints. Once filled with tools, this thing is going to be very heavy, and expansion and contraction is also going to affect it, particularly if the owner lives in a changeable climate, especially if the box will be stored outside.
With that in mind, I'd probably be very practical and make it from plywood.
The more I do, the less I accomplish.