Methods of adding ballast to underweight robots

[vivek16]

I'd like to start this discussion up again. We are underweight but also have skewed weights over each wheel. I've been thinking of riveting 2 foot long pieces of 1x1 (sealed on one side and removable cap on the other) to each corner "tier" (vertical beam on the bot that essentially form a box) and filling them with steel or lead shot. This way, we can quickly add more or less shot to each beam on thursday to adjust weight with each wheel resting on a cheapo bathroom scale.

Any thoughts?

thanks, Vivek

EDIT: What sort of store would have lead or steel shot locally? I know Mcmaster has it but shipping will be ridiculous.