Boost231, I TRIED to put my overflow in the spot you have yours and had no luck what so ever. It wouldnt fit in there, as in it wouldnt fit 100% in there, one side would go in, then the other would, i said forget it and put it back in front of the battery.
It will fall inside if you try to mount it there without the mounting hanger provided in the kit. If you look closely at Boost231's picture, you will notice he used the mounting hanger and it is screwed down next to the ground wires; very clean installation.