ORIGINAL: Gray Beard
Rubber bands. I spray my sheeting with a 50/50 blend of water and ammonia, let it soak for a while until it gets soft then I start bending around the fuse. It can be held with rubber bands while the glue sets up. If I can I like to use CA glue when sheeting curves.
I use laggy bands a lot too. The BIG ones for holding wings on.
Depending on what the task is, I use external strips of spruce or stiff Mylar (I use a lot at work) or even cardboard, to stop the bands cracking the wood or producing "sags" between formers.
EVEN THEN, I often need to build up the force at the edge of the balsa with extra thick strip, just to make sure it seats down and doesn't set proud.
I've never been a fan of steaming except for thin strip balsa. The ammonia is a good tip:- sends the cellulose all bendy for a time.