What are local users preferences on ways to limit rust on USB plugs? What do you use if anything. I notice some of my USB plugs rust faster than others in the tropics.

I have never noticed any rust here in Bangkok so not sure it is a tropic issue. Are you subject to sea salt in air perhaps?

Don't know if "rust" is an issue but I have noticed corrosion in general on many plugs/receptacles be it USB, RCA or just plugs in general. Usually just inserting and extracting the plug is enough to "clean" the contact area. Places like Amorn sell contact cleaner that could be used if more of a problem is found but be careful applying this stuff as it can degrade some plastics.

I have found very considerable rust on USB jacks on the computers on several diveboats. However, the four actual contacts inside the jacks are gold plated and good as new, particularly with just a bit of usage. The rust on the outside is unlikely to affect the contac quality.