Has anyone ever built a slab flattening router sled?

I have some live edge slabs I need to flatten and I am planning on using a variation of Nick Offerman's router sled:


Rather than use solid lumber for the rails, I thought laminating (3) 3/4"x6"x96" sanded plywood would be more stable. So I've got that done.

(It's still too hot here to work outside so the kitchen has been hijacked )

At the back of the plywood table is the sled that will go between the rails but I still need to make something like the boxes that lay on top of the rails as in the first photo. I have a number of thoughts but would love feedback for anyone who has ever built a sled such as this.

Right now I'm thinking of using aluminum angle to rest the router plate on. This is the bottom view:

I was thinking the open area will give me a better view of what I might have missed. But I'm wondering if the dust created by this process might be worse with the bottom being open. The parts are not glued together yet because I'm not sure how this will work.

Thoughts?