Hi Kail,

You can get lead weights from a place that balances wheels for real cars, usually they have 7 and 15 gram weights with sticky tape on the back ... hpi also do slim weights in different sizes.

I squeeze 20 - 30 grams inside the front and rear bumpers, then 15 grams per side above the battery (between the battery clip and the chassis), and then another 30 - 50 grams goes inside the chassis just behind the battery.