I went through this some years ago, with a couple of lessons learned.
Most of all, I would recommend using a good contact cement to adhere the material to the little panels. I tried several adhesives prior to that, and none of them worked well. The material does need to be stretched over the curved portions of the pieces, and the last thing that you want is the material shifting as it dries - it is hard/impossible to clamp along the length. The contact cement worked great.
I also got some stuffing from the local sewing/handicraft shop. It was not foam, but more like loose fleece (hard to describe). It was really easy to put small amounts of it where you wanted a little additional padding. If you were to adhere one side of the dash panel material, it is easy to put what padding you want in place, pull the material tight on the other side and see how it looks. I ended up using very little padding, and it does make the dash look clean. I used the same padding material on the top part of my seats to take up the slack when I did them several years ago, and it still is great.
Regards -- Roger