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Two sided tapes come in different sizes and brands. 3M is obviously one of the better brands. DON'T go with some cheap Walmart crap.... it'll bite ya in the butt later.
Use degreaser and wipe the door down and backside of mouldings. Lay some masking tape down the side of the car once you've established the correct placement of the mouldings so you can keep it straight.
Warm the mouldings as you are putting the tape on mouldings. If the tape you use is wider because there is nothing the correct width, place the MAKER'S EDGE against the TOPSIDE of the moulding. That is so if you trim off the excess and it's not "perfect", no one will see an uneven edge from the bottom of the moulding... however you'd see it viewing it from the top.
Once you've got the tape on the mouldings, heat the panels to warm them up prior to installing mouldings.
Gently set the moulding on the panel without making it completely stick. Once you've got them where you want, then go back and push tightly along the moulding.