As long as the dash is out of the car, any sander will do, but if you have a pneumatic in line sander, and a DA for the finish work, I would think that would work really well. It won't take a lot of grit to sand it down, just do a little trial and error. If you can't find any 1/2" closed cell, I have a supplier that has it. A yard of it 60" wide would be about $30 shipped directly to you. I don't know if I can buy less than a yard, but I'll check. PM me if you want me to get it for you.
My next question is do you really have to sand it at all? I'd use 1/4" for the whole thing if it doesn't matter.
No one lives forever, the trick is creating something that will.