Awkward body analysis:
He has extremely narrow shoulders. Even if he put on significant weight, he'll end up looking like peak Joakim Noah in a best case scenario.
Good news is he has a pretty decent amount of muscle mass in his hips and butt, so theoretically he has some decent stability and core. If he fills out his quads, he should be okay.
Bad news is his hips are like 5 feet above the ground, limiting his strength in the post. He'll never get his center-of-gravity lower than his defender, pretty big detriment to his leverage to push defenders around.