As Alex says we have welded the HDPE shell on Aftershock and it has stood up surprisingly well against the spinners. We did have a proper plastic welder on loan from my uncle but we had to give it back, we now use a special nozzle for a normal hot air gun.

You can pick up the nozzles fairly cheap, but I would recommend getting a decent hot air gun where you can full adjust the temperature so that you don't end up melting the whole lot.