Outer Limits 4x4 Board

Hi all, I have just fininshed prepairing my fj45 body for painting. I have a panel/box section U chanell that bolts on across the back of the cab just under tray height.
What is it for and do I really need to put it back on as I want a clean look on the outside ??

Thanks for any help on this part.
Scott

its not for bolting on the straps for the fuel tank is it? Thats the only thing i can think of that protrudes past the back of the cab.

its not on my 45,but i have long range tank under both seats,im not sure what its for,its on new parts cab i just got

I've got the same thing on my 76' FJ45 but doesn't have one on the 79' FJ45 also i have no idea what it is for either