powder, you dont have to go quite as gonzo with the material as you see some on some of the ones in the store. those look like that have 50lbs of material. im sure you can get away with not putting quite as much on and still get the desired effect, that should help keep it light and make it a little quicker to make. also, since itll all be covered anyway, try and use some type of lightwight material. i know a lot of the jogging suites that the major sports brands (nike, addidas, etc) make are specially designed to keep runners cool and would probably do the same for you, plus you can get most of them in black wich would be my choice for a base color to add too with the burlap and various greens and browns you use for the suit.
let us know how it turns out.
mike