Flatbed....rails? boards? keeping the camper centered...

What I did was use 4 pieces of 1 1/2" 6" long angle iron, measured where center of flatbed was and came out 1/2 the width the camper , drilled and tapped the angle irons down, placed about 1/3 the length of camper floor. Camper will always be in the center and will nor shift around side to side. When camper is unloaded, remove angle irons and bed is clean of anything to catch on. I used stainless bolts 3/8"X1".