Hi all. Ive got a bit of an issue with a 22mm gas supply pipe (after the meter) running in an internal concrete floor. Before I get a Corgi guy in I need to make sure the channel is correct because Ive got some other works to do before he could start. A channel has already been cut but doesnt seem right for this purpose. Its 25mm deep and a plastic trunk with lid clipped onto it, flush to the surface. I read in the other threads that there should be 25mm to the surface from the top of the pipe and the duct vented at both ends. Does this venting need to be external or is internal ok? Does it need to be vented if the duct is filled with sand? Does it need 25mm gap if metal trunking were used instead? Any info greatly appreciated! Thanks in advance.