This is a difficult question. I struggle with issues of trust similar to yours.
My body is always just a little bit tense around everyone, always just a little bit vigilant.
Yep. This is me, exactly. Sometimes I find it hard to believe that it's possible to be completely relaxed around people all the time. I experience it sometimes but not consistently, though I experience it much more than I used to.
I notice that when I am feeling more trust, that I also feel more confident -- not necessarily in control, but less caring about control. I feel a certain ease with myself and with others. My voice is fuller and deeper when I'm relaxed -- this characteristic my T and a couple of friends have pointed out to me. And I think that relaxed state is a trusting state for me.