Getting ready to build first car for cub scouts

We are running 4 oz. of Tungsten cubes. Two rows behind and two rows in front. To do this you need to get the body down to 9 to maybe 11 grams / .40-45 ish ozs. The stock wheels and axles weigh about 14 grams/ .5 ozs. This leaves a little wiggle room for paint and what not and a touch of puddy if needed.

What's the best way to hold the weight in? Thanks for all your help
 
What's the best way to hold the weight in? Thanks for all your help

Well, I don't know that this is the best way, but this is how my kids and I are doing this years' builds (currently in progress on the kitchen table...)

Start with our 1/4" thick body, cut out the tungsten pockets and the weight reduction areas with the scroll saw.

Cut a strip of thin 1/64" thick birch plywood (obtained at Michael's) and glue with wood to the bottom of the car. Clamp between two old car blocks until set.

Under the tungsten (and on top of the plywood), we'll put a layer of foam double-stick tape to keep the cubes in place. Then, we'll use some foil HVAC tape to wrap about 1/2" under the car, around the back and over the top of the tungsten cubes. Then we'll put the top layer (with graphics) over the top of everything.
 
We used Bulldog's router method to cut the weight pockets. Then we placed the weights. Then we we used silver foil HVAC tape to hold it in (like Vitamin K above), adding cotton or toilet paper/tissue under the tape next to the weights in any void in the weight pockets to keep the weights from sliding around.
 
Since Box Stock is not a points race Joel could make it a monthly money class. Have the option to send an extra $5 entry if you want. If you don't send the extra $5 your not in the money bracket. Winner takes it.
Hey Steve! Does this mean you're building a Box Stocker??? I like the monthly money challenge idea if we can get some interest...Cram, True North, Skywalker, BULLDOG, what do ya think boys?!!!
 
What's the best way to hold the weight in? Thanks for all your help

The wheel base on the car is 4 3/8" and with the weight in there the car seemed to have some waggle in the rear. Should I have center of balance on the car??