Well, here's my report of last night's virgin run of the Tamiya TB Evo 2 converted to Rally Car. My home track is primarily used by 1/8 scale buggies & MT's and has a hard-packed, dusty surface with a few bits of gravel mixed in. Normally, we don't notice the gravel because we run Monster Trucks which just shrug them off. A 1/10 Rally Car however, managed to find most of them.
On parts of the track that didn't have them, the Evo 2 performed as expected, drifting into corners beautifully. However, everytime it found the little stone bits, it would stumble and ruin my race line. Very annoying. The good news though was that my DIY undertray didn't rip or tear after numerous rounds, despite costing the equivalent of GBP 0.01 and 5 minutes of my time to make.
Except for a loosening diff which was easily tightened, the Evo 2 also didn't break any parts, not even a single popped off ballcup. Nevertheless, the caretaker said he'll have the track swept beforehand to minimize any distruptions. Also, despite no problems being encountered with dust and dirt getting in and disrupting the drivetrain, I'm going to make an overtray tonight to further protect the insides as per tonysmini's suggestion.