On tankers we often went overseas with a crew chief in the sixth seat. Over in the States, for example, it would all be first name terms. Also, with the crew possibly sharing 3 hotel rooms, one guy would share with the crew chief and no-one thought this was a problem.
Back home, down on the flight line we would revert to "sir" and "chief" once again without any problem or resentment. Seemed pretty simple to us.