It's taken a few rounds, but I think I've now resolved the last few trouble spots on the overall bodywork design. So let's call the design work for the TRX LMP done. (unless, as it turns out, a test build reveals there are still a few things to address)

The Traxxas LMP model got to see some simulated wind tunnel time. Autodesk Labs has a lightweight CFD simulator available for a limited time. It'll take a 3DS or STL model and run computations in a fixed-ground tunnel environment. The results are perhaps not absolutely precise but for my purposes insightful enough.

Test-build of the preliminary tunnel underfloor design. The Traxxas battery boxes angle up from a central low point on the underside of the chassis, so they leave some room for underfloor tunnels that the flat floor wasn't utilizing. The outlet end of the floor, and the rear diffuser, run at about the wheel/axle centerline. Aggressive, but effective...

Very rough build of the LMP evo body design using very crappy paper... Really just a fitment check and validation for the underlying model, but still can't help but zip it around on the street. This is the first time I've had a complete body, along with a useable wing and full tunneled underfloor running together.

The Traxxas runs really well with the light kit and an aero kit on. It's very fast and very stable and a good time, even in the dark.

After building a prototype of the twin-goose-neck rear wing and diffuser setup, it looked like it could develop even further. Also, the flat floor left quite a bit of unused room under the battery boxes which could be utilized for underfloor tunnels.

Running a very low, dynamically-loaded chassis requires precise spring and damping rates. However, the Traxxas chassis is optimized for off-road use with provisions for very long-travel suspension. Unfortunately this bias is exactly the opposite from what would be ideal for road use. In stock configuration, the front wheel rate to shock rate ratio is nearly 2:1, allowing a compact shock to take up a very long-travel load from the wheel.

LMP model needed another round of changes to accommodate some new aero ideas for the underfloor and wing-mount as well as correct some fitment and dimensional issues.

I intended to avoid any permanent modifications to the Traxxas chassis to accommodate my new bodywork concepts. However, there are a couple relatively simple things which could be done to allow for much more optimal designs.

As my skills improve and car speeds increase, the little Traxxas Rally's instability at speed is becoming an issue. The chassis handles so much better without the bodywork on that I believe it's probably more than just a weight consideration.