Some hermit crabs display NO symptoms at all and will surprise you with a surface molt right in the main tank. Protect your crab by cutting the top and bottom off of a 2 liter pop bottle, then gently push it down around the crab. Push it all the way to the bottom to prevent other crabs from climbing over or digging under. hermit crabs are known to attack and canablize a defenseless molting crab. Do not attempt to move or dig up a molting crab. Do your best to protect it and let nature take its course.
If your hermit crab surface molts in your ISO tank, simply place a coco hut over him to offer him some privacy. This will reduce his stress when you open the tank to change food and water.
Some crabbers, myself included have had many successful main tank molts.
I do not recommend misting a surface molter. There is a risk in doing this, in that it could promote bacterial growth. If your humidity level is in the proper range, there is no need to mist.