My Thomson rail bearings are continuously supported. The bigger 1" one is supported by a trapezoidal rail with a 1/4" NC bolt threaded into the rail every 6". The part of the support rail that is against the bearing rail is actually triangular in shape, so the rail is centered. Part LSR-20PD.
The smaller 0.75" rail are support by an aluminum T extrusion with bolts every 4"