Sorry about not posting, I just can't think of anything other then annihilating bat's that my Char would be doing, and since he's pretty far away the only way for him (and accompanying Ork's) to get to you guys quickly enough would be to go THROUGH the Castle (WALLS) and Castle's are mostly stone being held up by it's own weight, that would be bad.
Nice pic, Not quite what I had in mind, but it actually looks a little better then the basic design I had thought up... You forgot the Storm Bolters though, think Grey Knight style, only on a Power Fist.