If I was you, I would have reversed the AB and C pads, I always put the controls as far up as I can so it is possible to put my shoulders on the top and not the back, and then I have space to hold the portable with my palms under the main face buttons.
I've been using ABS cement for strength and to fill in large holes, and I always apply way too much. I can definitely sympathize with how much sanding it takes. I'm going to be using a putty knife to smooth out my surfaces before they dry, so that it's already pretty smooth.