Yeah, they will lose a lot of weight and most prefer to spare them the ordeal. They work really hard. It's something to see and worth doing for the experience, I think.
You have to create less-than-ideal conditions when maternally incubating so that the female has some control over the conditions of the eggs within her coil. The tub has to be a little cooler and a little dryer than perfect incubation temperatures. She will tighten her coils to keep them warm and humid and relax them to let it out. She can also do something that is essentially shivering to generate heat for them. Yes, they can shiver to produce their own body heat! You want to have a backup incubator running the whole time and be ready to pop one or all the eggs in there any moment if something goes wrong. You could have a roll-away or she could abandon them for some reason. Some will eat during this. Maybe on the coil, and maybe they'll crawl off for the meal. Give them something smaller than usual if you try so you don't make them unable to coil the eggs.
Maternal incubation is the keyword you're looking for. Do a search here. There are one or two really good threads where I learned all this.