You might review the ideas presented here. I had a similar problem in that the table itself is severely crowned… over 8mm center to end and center to edge.
These supplemental rails seem to have completely solved the problem of the low rider following that surface, and in fact provide a reference surface for flattening the table itself. The crown is so bad that using 1/2" MDF for the spoilboard would leave less than 1/4" at the extremes after flattening it.