I think that yout Gemeni is a south african make, is it ?
In this case, the manufacturer uses a local glue to assemble pvc to hypalon, or pvc to pvc, or PU ..., which is perfect but very hard to get because it cannot be sent by airmail flamable, dangerous).
It glues very well, and very easy to use - a dream for all peaople who had to take care of the parts sticking together inadvertently ... I know !
apply the glue, 2 layers, connect the parts to be glued, then heat up to 70°cent. with a heatgun. That's all.