If you looking for added storage, look to wasted space inside. Pull off some removable panels and see what you can do with that, folks on this forum, along with myself, have had great luck with that.
For exterior storage, look for a tongue box if you have room. And if you are feeling adventurous, there is a ton of waisted space under the trailer. Impersonally am looking into building metal frames the same depth as the 'I' beam frame that will house the large, thin, ammo cans on their side.