Bruce makes a lot of good points, so I can add only a couple tidbits.

I've been using the Harrison Original Tent in bright sunlight for changing my 8x10 holders, without any problems. As part of my "tent workflow" I always make sure all film is covered before inserting or removing my arms through the sleeves.

Picnic benches are a favorite place for me to change film in the field. I always carry some paper towels to wipe the bench off before placing the tent on it. I also carry several cans of Dust-Off to clean off the bench as well as blow off any dust on the film holders. Chem-Wipes are good for cleaning the hands off before handling film.