You are not going to hot air weld crossliked PE. The plastic molecules have chemically bonded to each other and a hot air gun will not break these bonds, allow more material to be introduced, and reform the bonds. Older PE boats did not have the plastic crosslinked. This is why you can repair them by heat welding.

As mentioned before, crosslinking is a double edged sword... They are very tough and can take enormous amounts of abuse, but once you finally break or wear out the plastic, it's pretty much over.

The crossliking is also why not much sticks to the hulls.