I've ran these tubes for two years now and they have worked well in my gmaxx, revo and my mbx5.
As far as the gmaxx chassis, they will fit, no problem. I ran two ten cell packs(took a little work to get the steering servo clearance and the velcro straps around) but you can fit 8 cells on each side with little to no problem. With the andersen/sermos connectors, you can easily connect multiple packs together in series.
Here's pics of my gmaxx with the tubes:
I know the velcro straps should go the other direction but I wanted to run 20 cells and didn't want to run with the extended chassis.
Yup, thats a tmaxx transmission on that gmaxx. Automatic 2speed, gotta love it :D
Cheers