Unless a rig spends significant time not moving in daylight, I suspect the tow cost and other inputs to a PV attached to the rig is above the ROI for power.

It might mean the cabin AC can run when its parked, and keep things humane. It might supplement a refrigerated intermodal and prevent engine run-on so be good for noise.

I doubt it would extend range much.

Happy to be proved wrong. E.g. the entire truck-top surface area with an integrated trailer might be enough to make sufficient KW to be worth doing.