unless the panel goes all the way down to the bottom of the belly there will be a pressure discontinuity 'kink' as Hucho calls it,which will compromise the drag reduction.
The wing may be in a stalled area of turbulence and not be able to divert any flow.A nearly-full belly pan might be required to clean up the flow enough for a wing to work down there.
Pickups have some of the highest drag underbodies
If it did,Hucho says that it will cause more harm than good,due to the drag of the wing itself.He tested a lot of aero accessories while at the VW wind tunnel and never saw any sort of flow diverter improve drag.