If I give any advice, it's really only worth something insofar as it reflects my own personal experience.
Anything beyond that is mere guessing. At least I admit it!
What I did was become an active member of my SSPX chapel for the 8 years before the SSPX crisis broke. My wife and I both had volunteer positions, I took care of the chant during Holy Week, etc. Both of our positions also involved working with our priest.
We made lots of friends and acquaintances, and most good people at our chapel got to know us and even like us. Some people we just don't get along with -- not necessarily our fault. Remember, some people didn't get along with the saints either (not saying that I'm a saint, but you know what I mean: basically you can't please everyone) And there are always human personality conflicts.
Anyhow, since I had such an entrenched position at the chapel, I could be a bit more bold talking about the SSPX crisis with people. Before long, pretty much everyone knew where I stood, and that there was a Resistance chapel being set up. A few people spread the word to others.
I wouldn't want to be in the position you describe -- someone who comes in for Mass, leaves, and only be known by a few other people. I don't know how I'd spread the word about the Resistance in such a situation. It would be an uphill battle, because people would rightfully ask, "Why should we follow X -- what has he/she done for this chapel? They're an outsider, they never really supported the SSPX to begin with, etc., etc."
Whereas many of our friends at our chapel know that I was in the seminary for 3 1/2 years, we used to stay after Mass to talk to people about CathInfo-type topics for hours, we signed up for the choir the week we joined the chapel, my wife helped with the accounting for several years, etc. We really look like we're involved and truly love the SSPX and our chapel. It makes people stop and think, at least for a minute, before they outright dismiss what we have to say.
Of course some people still probably talk about us behind our backs (supposedly 8 people wrote a letter to Fr. Rostand, which got us both fired), but you can't really stop that. Some people will be jerks no matter what you do.