I was thinking about that while driving to work. You can use pieces of leather, hardboard or thick cardboard between the wedges and the body to prevent dents as those will spread the pressure on a larger area, thus preventing dents. You can make the wedges out of any wood although I'd prefer some dense hardwood like maple or beech. Pine might split under pressure. Having all sorts of wedges at hand can be very helpful, make them wide, narrow, long, short, tall... And save them for future use! The illustration just shows where to put them, not the actual shape or size.