According to the exterior dimensions diagrams that FWC sent me, the distance from the base of the camper to the main overhang is 21.5" on both the Hawk and Grandby.
Edit: I just measured our Grandby and the distance from the bottom of the camper floor to the overhang is indeed 21.5". However there is an additional ~1" set of risers attached to the floor of the camper to lift it above the bed rails on our F350. So the actual height is 22.5". This will probably be different depending on which truck the camper was built for. However, i think you would be safe with the 21.5" number as the minimum.
Edited by heinphoto, 02 December 2020 - 03:25 AM.