Salam
Brother, I try to find a “single” bathroom even if it’s for disabled, and try to be quick so that someone deserving does not have wait.
Other times, I stay paak so that a second wudu is not required. Failing all of that, I do the wudu in public places, and if someone is there I tell them “pardon me, I’m just cleaning before my prayers.” That has never failed me. There have been times where the guy stayed at the bathroom watching me do the wudu and I took the opportunity to do a little dawah by explaining why I am doing this and the purposes for ablutions. Never had anyone give me a strange look forget calling security 
All the best!