How should I glue on a patch / rubbing strake / grab handle?
First of all, know which materials you are trying to glue as they need different techniques.
Generally you need to prepare the surfaces so they are clean and free of grease, apply a thin coat of the correct adhesive to each item and once the glue is dry, to push the two parts together.
Gluing PU tubes
Glueing Advice Please
Glueing PVC to Hypalon
Gluing PVC boat fabric