I have used RC56 successfully for years on canopies but am now finding that it doesn't hold well on canopies in some ARF kits. Perhaps its the canopy material or the fuselage covering material. Have also found that these canopies can't be dyed with RIT dye. I still use RC56 but have been using small screws and/or trim tape to backup the glue.

Goop and Seal All have been suggested in this thread and I might try those on test surfaces. Thanks for sharing your discoveries.