I too, have been contemplating selling my slide-in 2015 Hawk for a flatbed Hawk.
The one problem I'm am having, and probably will not get an definitive answer until Overland Expo in May, is the rear over hang of the Hawk camper aft of the flatbed. I often carry my motorcycle with me in a Joe Hauler hitch carrier. Just by looking at the photos of the many flatbed Hawk installs, it seems the motorcycle handlebar would interfere (contact) with the rear, vertical portion of the flatbed camper.
As I mentioned, this may be an illusion in the all the pictures I've seen. I will likely need to get some measurements or install the carrier on a flatbed Hawk/truck at the Expo to get the straight skinny on the perceived issue.
Definitely do no need a headache bar on a flatbed dedicated to a camper.