I'm afraid the RPM steering knuckles hold the step screws in a worse way than the stock ones. RPM plastic is softer and more flexible, that's the way it's ( almost ) indestructible.
I suffered the lost of the step screws twice with the RPM, and took the piece of advice of a guy in the missing (and missed ) URC forum. I've bashed the hell of my Ruckus since then, no problems so far.
IMHO there's two ways of forgetting about losing steering screws. One, use rear knuckles as in the picture ( not necessarily RPM, stock ones serve as well) and some spacers with a longer screw and a locknut. Two, get some aluminium/aluminum ones (depending if you're UK or US...) and some blue threadlock in the steering screws.
I don't like "purpose made" screws like the ones in the steering, less if they're prone to get lost easily, and it's still worse when neither your LHS nor any hardware shop stocks them when you need them the most...
I almost forget to add that you need metal turnbuckles with the first option, usually Team Associated or Traxxas do the work.
Sorry for the long thread and about my English, I'm Spanish??.
Hope it helps.