Originally Posted by nine4gmc
i am body dropping a yukon and it is common to use 3"x5", 3/16" box for the rails, this is a large heavy suv though and requires the thicker wall. i would think your 3x5 1/8" could work but lets hear from some car experts.
I think he is planning on using 5x5 1/8"
I think it will work ok, but I think what you are using( 3x5 3/16") would be better