Hi Marc, My approach to epoxing and sanding is a bit different. I have a large fan in the front door transom, the back door has the bottom panel screened (about 30"x30" since I live in Florida it doesn't have to be sealed), I wear my mask when I am glassing and joining the hull to the deck but not when I'm fill coating ( it just doesn't take that long to fill coat).when it's time to sand I move the boat and saw horses outside and arrange the boat so that the wind is at my back so no mask is needed when I finish sanding one side I then flip the boat.I am not advocating not to use a mask your health and personal preferences should be first.Please be safe and have fun. Nick R.