zaccutt
+1y
12 is basically 1/8" and would definitely weigh your truck down like a mofo. Like they all have said I would go with 16 but it is pretty hard to bend unless you have good bending tools. 18 may be a little harder to weld if you have a lower end welder that heats metal up more. So if you are planning on doing a lot of bends go for 18 if not go for 16..
Zac