Forty years or so ago, I got some salvaged pine from pallets where I worked to make a box for my reloading supplies. The boards were all cupped, so I just cut rabbets for the ends and nailed the thing up with the convex sides out. The joints are straight and solid and the box has a bit of a treasure chest look to it. It does have corners that need to have a filler strip nailed in. Some day, I may get around to doing that and sanding the whole works and putting a finish on it.

My point is, a box can look pretty nice with convex sides.