I'm getting error code P0455, indicating a leak.

I'm getting error code p0455, indicating a leak in the EVAP control system. I just spent a ton on other repairs and would like to troubleshoot and try to fix this myself. I replaced the gas cap and had the check engine light reset. It was ok for about a week, then came back on with the same code.
I've read about a "smoke test" - have no idea what that would cost. Can you tell me how to track down a leak myself and what I might have to replace? It's not really covered in my Haynes manual.