plastic welder for gas tanks

I put a tank from a '73 W300 into my '72 W200 and then found out it had a crack. I took it to a local RV dealer and they plastic welded it about 15 years ago. No problems so far. But I have noticed that there seems to be more than one kind of plastic tank, the 'smooth' ones and the 'hairy' ones. Mine was smooth and apparently welded well. The hairy ones, IDK.