Here is the "under bed" fuel tank for 1954 panel-body trucks (Panel, Suburban, Canopy Express).
My uneducated guess is that the panel body "bed" is no lower than a pickup bed?
47-53 pu-beds and panel-body-bed might be different in "clearance".
Let's hope that someone reports/replies who has done this on/with a pick-up truck (please state the year).