battery pack on receiver
1) Radio Manufacturers recommend keeping any Power supply wires as far away from the RX as possible.
2) The RX Pack is in the Rear for a reason, weight transfer to provide more Traction.
3) Lastly, the weight of an RX pack is considerable and with mounting it on top of the Receiver, a hard Chassis slap on the ground could be enough for the Receiver case and internals to be damaged.
Just my thoughts on the subject.