Here are a couple of photos of my jig which I made recently but not used yet.

Note that the clamp bar is only notched at the LE to retain the rods, the other end is plain to allow any rib length. An intermediate clamp and 2 extra supports are there to stop rods sagging as I used 5 mm steel rods (smaller than 1/4 which is 6.35mm ). The intermediate clamp is loose & is used for wings that are less than the 48 inch length of the jig. All the wood supports were prepared to exactly the same thickness. I drilled clearance hole for the bolts right through. I used nut inserts but hexagon nuts could be used underneath, in that case measure the distance across the flats and enlarge the hole to that size for the depth of nut. The ‘corners’ will cut their own way in when you draw the nuts in on the bolt and hold themselves in. Wing nuts are used on the bolts instead of using a spanner.