Adding weight to the Supastox

[CAT3K]

I need to add weight to my Supastox (approx 30g under weight)

At the moment i've added a bit to balance the weight of the ESC, but i need to add another 20g. I fitted the lighter alloy axle so i think i need to keep the weight towards the back. So i have a choice of adding it just behind the lipo on the chassis, or underneath the motor/axle on the pod. What's the consensus on where to add weight in this area, sprung on the chassis, or unsprung on the pod?