On the whole, super glue (one of many common products ... This kind of plastic doesn't work with super glues very well, so Loctite has developed a two-part plastic bonding system.

Epoxy adhesives often come in a two-part arrangement, typically a resin and a hardener. Loctite has a product suited for a vinyl fence called Plastics Bonding System, which sells on Amazon for $27.38.