If you ever had to flatten a slab or large piece that won't fit through your planer or something that would need too much hand work than you'd like, Usually most people would build a simple set of router rails.
Nowadays they have them ready to go but for a rather hefty price. IMO
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I just got my Lee Valley Catalogue and they have a very clever solution that keeps the price way down
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You still need to do some assembly but the result should be a much smoother movement than simply wood on wood. (sled on rails)
I may have to give this system a try next time the need presents itself.
Just though I'd share

Ok... I cheated. A  guy about 30 miles away owns a shop that does a lot of woodworking and around Xmas, he bought a 4x8 ft CNC machine.

By late January, he was set up and I took a big sab of Claro Walnut burl to him and he used the CNC to flatten both sides and then he put in his massive sander and sanded both sides.

He said he only took about 1/8" off each side.

So... all you need to do is buy a 4x8 ft CNC machine and you're all set!!

My JCPenney card??

It'll work as well as any of my other cards!!

Oh... you knew about that, did you?