I posed this question to my husband, who has a lot of mechanical experience. He says most computers are so well built you can completely submerge them and they'll be fine - as long as they do not have any electrical power! The problem comes when you have water and electricity mixing. He said the scenario posed here - condensation forming on/inside the machine - could be possible if you live in a very humid climate, or possibly near the ocean with fog coming in at night. But you would know it, because the condensation would be on everything; the sewing machine; the table the machine sits on; the window sill, etc. He added that it would be highly unlikely and he thinks it's not worth bothering yourself over.