thanks for the input. I recall seeing the supports on the Jessem phenolic router table with built in lift. Interesting that Jessem did not have these on their prior phenolic table. If Jessem selected aluminum, I trust it will work. I thought aluminum would be more likely to stretch and sag than steel. Even so, getting a dead flat piece of aluminum would be much easier anyway, so aluminum wins.
I have a 3/4 baltic birch flat base with 3/4 inch phenolic top. It will support an incra Master II lift, Porter Cable 7518, and Rocker sheet steel box. Put it all on a scale and got 36 lbs! Furthermore, the inside rail measures of the stand are 21x16 inches unsupport. Think it best to reinforce the belly from sagging.