I just recently realized that the STS .21B crankshaft is steel. Are all .21 cranks made of steel?
Isn't that a bad thing? Does rust easily form on them? The reason I ask is because apparently, RB mods does a "secret special treatment" to the crank shaft that is supposed to prevent rust and was wondering if this is necessary to protect the engine.

after run oil should help.

I know to use after run oil! That doesn't answer my question though...

RB's "secret special treatment" as you refered to it is a hard coating that is only in their high end motors. No matter what brand motor you run, you need to use after run. They all have steal cranks. The best practice is:
Run you car out of fuel on the last tank.
Clean around the glow-plug with your favorite motor spray.
Dry off the motor spray.
Remove the glow-plug.
Drop in 8 or 10 drops of after run oil.
Re-install the glow-plug.
Turn the motor over a few times (some guys put it on the starter box, I just do it by hand with the plug still loose).

Running the motor (& fuel tank) dry removes the fuel. Left over fuel attracts water & will speed up the rusting of the motor. The after run oil will coat the inside of the motor & inhibit the formation of rust. If you want your motors to last you need to use after run oil. The cleaning of the glow plug area before removal is to prevent dirt from getting in the motor when you take out the plug & put in the oil.

Answers:

1. No. Steel is good.
2. No. Regular WD-40 + ATF oil will protect your engine fine.

thanks for the clarification, guys!

yes every engine still needs rust protection but ok fellas lets all stop using WD-40!!! IT IS NOT A RUST PREVENTER!!! You are not doing yourself or your engine any favours using WD-40. Its totally useless ok!

What you want to use is a fa superior product called INOX. Use this. This is the bee knees of lube/rust preventers. I cant recommend this highly enough. I race yachts and this is the ONLY spray we use. Ask a good mechanical engineer and they will say the same. WD-40 is total garbage.

you could even use some Mobil 1 synthetic oil as a afterrun oil actually works better than most oils and displaces moisture.

Im with mozzzy_2000 on the inox. The old adage goes if it dosnt work use a bigger hammer, with me if it dosnt work .. use inox. I doubt if its exported to America though unfortunatly

i can't always run out the last tank but i start the car on the box with the fuel lines disconnected, then i plug'em up ready for cleaning. i hae heard of people using 3in1 oil instead of aro but i mainly use 5w30 in a small bottle and i drip it through the exhaust with the engine off, couple turns (i like to face the engine down to get the front bearing good) and plug up the exhaust. then simple green+brush+air blasts. she'll sit through the week till saturday morning or friday night to bolt on truggy or buggy.

If you can't run out all of the fuel out then use your fuel bottle to remove it. If you leave fuel in the tank condensation / moisture will build up in the tank, and when you run you vehicle the next time you are running that moisture through your engine. Be careful not to over oil your engine if you use a starting system that requires a oneway bearing, because you can cause the bearing to start slipping. Same thing if you run a fuel with a high castor oil cotent.

I have been dealing with engines 35 yr's now,both land/sea. I agree wd-40 is better than water-but not by much.I have heard of the INOX just never had the chance to purchase it in the states.
What I have found to be very protective against moisture is Marvel Mystery oil.You can buy it everywhere and it's inexpensive...

Marvel Mystery oil, 3 in 1, air tool oil

Totally useless. If an engine is taken care of it will not rust inside.

Ooops, didn't see that I already posted here before.