I've always advocated the use of a fan going while while outside at the scope to keep the mozzies at bay.
And now here is the scientific backup for the idea.
Been doing it for years. Anyone that has lived in the tropics knows it's effectiveness too. If I have an option to use a fan, there is no known way on Earth I am going to apply some chemical to my skin! (I'd rather be bitten anyway than slather with DEET!!!)
I've known for years from camping that you don't get mozzies if there is a breeze. I'd never though of using a fan when observing, but then again mozzies are only an issue down here sometimes in summer, and the long days tend to curb my observing then anyway. If there are mozzies they tend to be worst around your feet and ankles, so I wonder whether it's best to have the fan at ground level or up higher?
If my feet are bare, I'll still spray my feet. And apply some on my face as well as I hate it when they get trapped behind my specs.
But the less of that crap you put on your skin the better.