wanting to put 18 in wheels on rear of truck, how much do the sides of box add to fen

[Houdini]

from the bracket in line with rear end on side for mounting the box how much does it space the rear fender out
got the moser rear and std brakes and I come out to 4 in back space on using a 18x 8 in rim any suggestions would it hit fender on outside edge??????

I really want to run smaller rims got 16 in but want the big and little look so I am thinking on going to 18 in rears

[rponfick]

I get about 13 1/4” out to fender inside lip from bed panel. Add thickness of side panels, as I have mine mounted, to get to frame mounting bracket. Panel is about 1/4”, but I cannot measure currently.
Hope this helps.
Ralph