How do I heat an outdoor crawl space which has plumbing pipes running through it?

I have an added bathroom which is set above an unheated crawl space. The "ceiling" of the crawl space has all the pipes running through it (hot, cold, waste). These pipes had been insulated with your standard pink panther blanket insulation but the pipes would freeze anyway. I am thinking of putting some sort of heater in the space to keep the pipes above the freezing tempertaure. Does anyone have any suggestions on what type of heater I could use, or another method to keep these pipes from freezing? Right now I have electric baseboard heating the bathroom and a constant drip on both the hot and cold water lines, which is obviously a temporary solution.