I was skeptical of the straps providing enough lateral support when I first installed my chassis (I love the chassis, btw).

The gmaxx straps are fine if you have something else that will provide the lateral support necessary to keep your batteries in place. Granted you would think the straps should be enough, but I had the same experience as yourself. Used zip ties, extra velcro, etc. Nothing worked solidly enough until I decided to make the cups.

If you read my post above you'll see that a very inexpensive and easy to craft solution is available. You're looking at about $5 and an hour of your time. Oh, you may wanna sand the cups and paint 'em...so another $3.

Maybe you'll come up w/ a good enough design and can market the N-maxx cups for the g-maxx chassis, sell 'em for $10. :D