Mesh Colliders With Terrain Not Working

I am trying to use the terrain's paint tree feature to mass place rocks around my map. These rocks can't use any of the primitive collider shapes because they are slightly more complicated, so I'm trying to use the Mesh Collider. My character is using a capsule collider, and it can collide fine with the rocks that are placed one at a time manually, but any rocks that are placed using the terrain, my character just walks right through.
My question is should I be placing my rocks using the "paint tree" method in the terrain to begin with? And is there a way to make the mesh collider with these rocks work with the terrain? It would take way too long to place them manually. I have tried setting the mesh colliders on the rocks to convex but that didn't change anything. Any suggestions? Thanks.