door/quarter panel skins

how do you put on a door skin. should i just take it and put some fiber glass on the back of it and stick it on the existing panel? or take off the existing panel.?

i believe you have to take off the original skin and use the original bolts/screws to screw it back on..i hope we're talking abt 3rd gens, cuz ive never taken the skins of anything else..

the fender skins are easy to put on/take off..idk about the doors and quarters