I agree with OCD. As long as you have the 4x4 posts mounted you should have plenty of support along with the 4x4's going the width of the trailer but it would be up to you if you wanted to like OCD said. I would look into a 6x12 also when shopping. When I had my trailer built I went with a 6x12 because it was only about $100 more but it does add a little weight but wasnt a big deal to me personally. Not sure that may also depend on location the prices just something to consider. Mine in the pictures above had a lot of added features. I went with aluminum wheels, screwless sides, two tone color, v nose with the wedge, one piece roof. All things to consider because that is extra but once again not a have to have.