I've been taking my time trying to get the rim just right. I'm using 2"x2" with radii (radius plural?) cut into them, and sand paper applied to the radii. I spin these sticks around and sand the rim, so that the radii are transferred to it, which will match the radii of the top and back.
The work has been pretty slow going, as I don't want to take too much off of one side. I think I've pretty much got it pretty close, except for the "shoulders" on the back. I have more to take off there, and then I'll need to notch the kerfed lining in order to insert the bracing.
I didn't anticipate using the cradle, that I built to go with my binding jig to sand the rim, this way. But the mold fits right on top of it, and with the height adjustment, I'm able to make it level. I mounted that little 1/2" metal pole in the middle of it, and it worked out really well.
I may use this same set-up to glue the top and the back to the rim, also. We'll see.