I don't know if it would work for you, but my local lumber yard carries 5/4 T&G yellow pine, and it worked pretty good for a trailer I built. Not quite as heavy as the 2x, but more than adequate for the hauling I do. And it seemed to warp less that the 2x treated.
I put a good coat of black paint on all the boards before I installed them, and it's held up well for ten years.
Tim
I am currently digging back in to a 1953 3800 (one ton) with a nine foot bed. I've owned it since 1979, and drove it until 1982 (or so). My wife got me involved in restoring it back in 2002, got the body removed and the frame redone, then things came up. Now I am retired and starting again. If anyone is interested I have photos on Imagur (
https://timwhiteblues.imgur.com/ ). I live way back in the woods in the Ozarks on 40 acres at the end of a 2 1/2 mile private road.
Tim
