I've actually used some Flextape for a minor repair on my slide. Whatever kind of tape they used to cover 2 joints in the slide outer frame failed rather quickly, so I replaced one section with flex tape. So far it is doing quite well (about 5 months now in both tropical and desert climate). Guess I'm now kind of doing an unintended experiment.
Know that if you read deep into the very, very fine print on the Flextape package, it states that the tape is for temporary repair only.
So far I'm impressed, but not sure I would trust it for a serious repair.
Eternabond for anything serious.