Thanks, John. I made the sides of the sled tall to minimize sag. I suppose I could do what you suggested and double laminate one side. The reason I didn't question the Offerman method of holding the top of the router is I thought there would be times I would be unable to reach the two handles on the router. I thought that's why Offerman used the top hold method.
When the sled is close to the end, I am able to get my hands on both router handles but once I'm about two feet from the end, I can no longer do that. I could lower the legs on the sawhorses. Will have to do a dry run and see how that goes. But you make a great point the router will catch at some point. Better safe than sorry.
I was going to make the wing box with a bottom but I didn't think the plywood would slide all that well, even with a few coats of poly. What I was thinking was putting plywood on the bottom and covering it with a sheet of 1/4" UHMW. The reason I made the wing box so wide is I wanted to reduce transferring any imperfections in the rail onto the slab.
Anyway, here's what it looks like now:
The UHMW are only 3/4" wide so that kind of defeats that transfer issue I was trying to address. And it doesn't slide nearly as well as when the UHMW was parallel to the rail.
One thing I do like is there is plenty of room to tighten the knobs
But dialing in a precise elevation will be tricky.
And I will have a good view of the work being done