This is a guess, but I'd assume the adhesive is designed for sticking to gel coat.
If I were apllying these to my RIB, I'd mask off around the area they were to be applied, thoroughly roughen the area, solvent clean, and give it a coat or two of hypalon glue (Bostik 2402 on your side of the pond, something like Clifton hypalon adhesive over here.) Should give it a better anchor to hang on to.
Actually, there are a couple of places I might want to apply these to. Hmmmm...