Me too
Well unless you already have the tube I would consider bumping the size up to 1.5''. Its stronger and will look a little more at home on the back of your truck. I'm guessing you don't have a tube bender since you want to use square tube so my suggestion is to go simple...
Do a flat deck, one that tappers towards the back like this one and just box it in a little bit. This is how I was going to do my bed before I had access to a bender. Hope it gave you some ideas.
