I had my van checked for gas safety just last month.Most of the threads relating to leaks I have seen have been due to defective cylinders rather than poor DIY fitting.
I had two Gaslow cylinders replaced under warranty due to leaking around the connector. My system was professionally fitted and always had an annual habitation service which included a Gas Safe inspection.
The guy says one pig tale neads replacing at sum point but apart from that he was very happy with my DIY
Bill