The Traxxas E-Maxx is a good chassis! I wouldn't mind getting one.
I did manage (I think) to figure out wheels, drive shafts and shocks for Traxxas (4907), bought some on E-bay. I'm only going to try 4WD (expandable to 6WD) for now. I do wish I had a better pix of the wishbone suspension parts used on the Traxxas. For simple, non-steerable wishbones and shocks, I might be able to manage and CNC some parts. Getting the shocks (spring over shocks) and the universal jointed drive shafts will simplify design (if the parts I ordered fit together!). I'm watching/looking for the wishbone parts, I can make my own, but they must be sized to fit the drive shafts. The remainder of the chassis fabrication, two geared drive motors and timing belt drive won't be hard. A good-sized project, 'tho.
What Sensor board will you use? You do know that the BotBoarduinos give you the same thing, with the I/O neatly brought out to three-pin headers? Greatly simplifies interconnects. I got mine last night! It is different from the UNO in that you MUST provide power. And for some reason, they want you to disconnect the USB while on the robot... I'd use SRF08 Sonars, more advanced then PING, less attention needed. I have an array of six SRF08 sonars, and a PIC processor to manage them if I decide to put all of them on the 'bot. 'Hate to steal the array from one of my MicroMoose 'bots.
I did find a $30 ESC that would probably work on the Hummer H2 R/C truck, it probably doesn't even need that. But I need a simple chassis to get navigation (waypoint) software work started.
I actullay built the complete Traxxas E-Maxx buy buying all the pieces off of various sellers on eBay. It took a while and was quite a learning experience. The most expensive parts were the CC NEU brushless motor and the Mamba Monster ESC! Unfortunately I do not have the machine shop capability to build the aluminum bulkheads and the assorted drive shafts and other hardware that DPA custom built for their rover. The Traxxas E-Maxx will have to suffice. It is very robust and the platform that I attached to the chassis in place of the plastic truck body has more than enough room for the Arduino UNO and the APM in one of the DIY Drones wooden boxes. Since the Traxxas E-Maxx is in Florida, where I plan to retire in about three months, and I am still in TX waiting to retire Aug 1st, about all I can do is order the Arduino UNO, Sensor Shield, and the three PINGs and two IR distances sensors and then proceed to try out the obstacle avoidance program.