well they dont look it but they are actually pretty good size. the crossmembers are notched for the crutch. you could ca a balsa strip on top which locks the crutch from falling out. if you need to get underneath for some reason ie threading tubing wires etc. the cutouts allow you at least some acess with needlenose pliers or whatever whithout a person having to take the fuse out of the jig.

I left them solid at first then got to looking and thinking of ppl wanting to run stuff and figured add some acess points at least for pliers without cutting too much out