If you wore a complete suit of full-body armor, would that hide you on the astral plane? I've always been uncertain about what blocks and what doesn't. If there's a thin sheet of metal between you and the viewer, no LOS. If you're wearing metal 3 times as thick, they still have LOS on you. Carry a paper-thin umbrella like was suggested, tada, somehow they can't see through that even though they can see through your super thick, non-organic, was-never-alive armor.