Can the smoke fan be supplied from the RL2C Board?

I don't think I'd be connecting extra stuff the the R2LC board, it's 5V is doubtless anemic.  It's used to drive the IR tether, but you may be asking too much for your fan, even though it's small.  I'd stick with the current solution, a three terminal regulator and a couple of caps will do the trick.  Well, I guess I'd add a diode for when the smoke boost is used to block the AC.  You could probably assemble these in a small lump and cover them with heat-shrink tubing.

Thanks for the reply.  Your comment about the R2LC supply being anemic is what I was concerned about.  The little 5 volt regulated supply I've been building uses a small full wave bridge rectifer so the AC problem you mentioned is taken care of. 

Since you mentioned it the AC voltage, with an 18 volt track input, do you know what voltage to the smoke resistors is normally supplied from an EER Cruise Commander?  When I first played around with the idea of using the regulator, my meter seemed to indicate there was a AC voltage superimpossed on an DC supply.  This surprised me.         

The smoke output is nominally a rectified half wave 12 volts, and it's full-wave for conventional running or when you use the smoke boost. 

The reason you see AC is that the half-wave DC will read as 7-8 VAC on a meter, however if you look at it with a DC 'scope you'll see that it's really half-wave DC.