I used basically office supply double sided tape which is probably not as good as the "real stuff". It did not stick that well to the luff tape which was very heavy dacron, so not that smooth. It did however last a full night and being transported in the car after.
The duct tape was not the branded stuff, but stuck really well to the sail and came off without leaving any residue. Because of the full battens there is quite a bit of pressure on the luff at the point where you are feeding it into the sail track, while hoisting or lowering, and this is where it let go a couple of times. I didn't do any sailing but think it would have worked. It seems to creep though when left under stress, and lets go over time.
If you search around there's a bit of info on taping sails together, especially for polytarp sails.
"Note: Rubber-backed carpet tape alone will normally last for a few uses without sewn reinforcement, but this adhesive eventually dries out and loosens from the slippery polytarp surface. Double-faced acrylic tapes tend to bond better with polytarp since the bond improves over time. If acrylic tapes loosen, they can usually be re-stuck.to the material. These more expensive tapes are used in our NO-SEW PolySail Kit.