OK, I pledged to lookup examples and come back with links.
This link is my initial LowRider build log, and it details my table both with wooden side rails at the start, and later switching to metal rails:
This listing of mine on Printables gives the files for the printed extensions I used to get more width out of the same table when switching from LowRider v2 to LowRider v3:
https://www.printables.com/model/220187-lowrider-3-cnc-table-extenders-to-use-lr2-table-wi
Finally, I later built another LowRider v3, this time for CNC plasma cutting, and the need this time was to extend length and add some “table drop” — with no real need to extend the width. The three Printables listings below were parts I designed to make that happen:
https://www.printables.com/model/415326-lowrider-3-cnc-plasma-cnc-table-parts-mounts-for-1
https://www.printables.com/model/415298-lowrider-3-cnc-three-remixes-of-rail-blocks-181-mm
https://www.printables.com/model/257450-end-cap-for-12-emt-tube-v10