So i was following the steps by my mesh does funky things when I used the convex hull and decimate. when going from the pin mesh to the convex mesh the top looks fine, but for some reason it decided to mess with the bottom. turning it into a funky square. then when I decimate it plays all havoc with the mesh.
Did you remove doubles before using the convex hull? It looks like the problem is where the curve reaches itself after the 360° extrusion.