I started with Conk soap and experienced the same drying out problems you did. It wasn't the Conk soaps fault because no soap is going to maintain itself for a 30 minute pass. When I started it took me an hour to do a single WTG pass. My solution was to lather only half my face at a time until I got comfortable enough to increase my speed.

As for your butt chin...I've got one too...you might be stuck with whatever technique you can work up for yourself. A good straight usually has a sharpened toe that is the perfect shape to get right into that area. All I do is to apply my thumb to one side of my chin and my forefinger of the same hand to the other side and kinda stretch the chin apart and then get that toe into the area and viola...clean butt chin.