EvilSOBs method only works if you got a mesh like a cube or a sphere
the basic idea is correct, but you can also have different cases of meshes:

The trace hits something (our gray funny-looking blob-mesh), but is NOT inside the mesh!
As i said you have to count all hits on this mesh. Even results (in this case 2) are outside the mesh, odd numbers are inside
this would be an accurate system to check if you are inside the mesh
and don't forget to active USE_POLYGON

For counting the hit targets you could use a contribution of me (Multiple Hit Traces)