Just wanted to show a few pics of how I achieve flatness on my router table (Woodpecker's top and Plungelift). The leg levelers located at 4 points under the top effectively make it possible to create any level of flatness you desire. All it takes is a few twists to adjust (up or down).
When I first built the leg system, I didn't compensate for flatness adjustment in the front and rear of the table so I added the crosspiece at the front...
and the additional "leg at the back...
I still need to poly these 2 pieces. The top can be easily removed by reducing the height of the levelers (to relieve tension) and pulling out the "pins" (knobs) at the 4 corners.