On my way back to the states from Spannibus this year I was traveling with a couple of vapcaps that we had used during our visit.
I cleaned them up before leaving and kept them disassembled and stored throughout my backpack.
I had no problems in Spain or the US, but let me just say that in Portugal they were very thorough!
In the end, no pun intended, I made it home with everything I left Spain with (except my dignity).