I always put my assembled PV (mod or otherwise) in the little tray with keys, change, cell phone etc. and nobody's ever batted an eye. I always keep a self-addressed padded envelope and sufficient postage in my carry on, just in case some TSA employee raises a stink but it hasn't happened yet. Much better to exit the line, stuff your gear in the envelope and mail it home than have you civil rights violated and personal property "legally stolen".
Packing a spare eGo or something similar in a checked bag is a good idea but I would never put even a moderately expensive mod in a checked bag.
Relax and don't be nervous; you'll be fine!