So on the advice of this thread I bought the 650D dust filter kit. Here was my experience with it. I couldn't use the rear filter because it was an exhaust. I couldn't use the side window filter as you can't filter a window! I couldn't use the front filter because I'd dremelled off the front fan grill so there was nothing to support the magnetic filter. The only filter I was able to use was the top one. So in essence I ended up paying £45 for just a top filter! I should have realised this before. Maybe it would have been better to get a top filter + custom front filter made by demciflex. Anyway, posting here to let others know of this potential pitfall.
P.S. Anyone know whether any of the filters on OCUK would fit the front (with the grill having been cut off)?