I was looking into the same thing. Limited options for the Outcast and Arrma RC's from what I could tell. Looks like carbon fiber and nylon are common options. There are adhesive ones and bolt on from what i've seen.
If you google rc aluminum chassis skid plates and protectors you'll see what I mean.
TBone have some for the xmaxx, 1/16 erevo and they do have one for the nero. The one for the erevo looks like it would work well. Would be nice if they made some for the Arrma model line other than just the Nero.
There's always the option of getting creative and developing your own based on some internet searches?