I have a 55 1 ton flat bed. I am making a new bed from 1/4 inch alum. plate and 4 inch alum. chanel. The wood that goes between the frame and bed was in poor shape and looks like rough oak. Has anyone tried treated lumber or should I stick with new oak.

 

Is the truck going to be exposed to the weather on a regular basis? My truck is under cover most of the time so I used untreated pine or fir lumber. I started with 2" by whatever to fit the original bed strips. I then put the lumber through a planer to size it to the original factory thickness. I then painted it black so when it gets scuffed with use I can easily touch up the paint.
If you are building the flat bed you can size the rails to whatever you want for the bed thickness. I think you can use whatever fits your purpose.. If you let the treated lumber age, it can be painted also.

 

I'm planning on using all rough cut pine (with a water sealer) on my bed and those 2 boards between bed and frame.

i've head that pine was the original wood used, and my bed isn't going to be hauling much at all. plus i figure it will save acouple $$$..........