A friend of mine put a steel flatbed with a headache rack on his shortbed Dodge. They also installed a B&W turnover ball. A shortbed with a sliding hitch is OK but now he can't use the sliding hitch and the headache rack takes another 5" away for turns. Needless to say but he has already crushed the front of his 5th wheel.
So if you go with a flatbed forget the headache rack.
2022 Silverado 3500 High Country CC/LB, SRW, L5P. B&W Companion Hitch with pucks. Hadley air horns.
2004 32' Carriage 5th wheel. 860 watts of solar MPPT, two SOK 206 ah LiFePO4 batteries. Samlex 2,000 watt Pure Sine Wave Inverter.