Cold surface into warmer moist environment is going to cause this and the only thing you could put on it to stop it is a large insulating layer which isn't practical. Otherwise you have to keep the lens, including the barrel, somewhat warm.
If it is going to be outside for a long time, an active heat source is needed. If this is a short term use, having the lens fairly warm before putting it into the problematic environment will work.
I learned quickly when shooting sports events in the summer that my cameras and lenses travel in the trunk of the car or the enclosed bed of my pickup because I like keeping vehicles very cool while traveling. Before this, the lens elements would fog and the barrels would act like a little dehumidifier for the first several minutes after I set them up.
Most importantly, after they attract all of the moisture you don't want them in a sealed environment until this moisture is gone. So if traveling, don't seal them in anything that restricts air circulation until they are fully dry. More than once, I have had lenses sitting on the heating system in my hotel room to dry them before packing them away for travel the next day.
Desiccant packs, particularly large ones designed to be baked at low temperature and reused, are very useful. I have several of the large cloth covered packs often used with military gear and these are about the size of a pack of cigarettes. A few of these will absorb a lot of moisture before they are saturated, the tiny little packs used in shipping consumer electronics products are too small to be useful when you actually have something that is already heavily saturated. Wipe off what you can then sealing in a bag with large packs will absorb any normal amount of moisture after which time the packs should be removed.
Rodger
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
