Hi Happy Hippy. Trace heating is fine, but there are two standards for it I've seen. One outputs twice as much as the other, per metre. It will not protect your pipes unless they are insulated as well. The thickness depends on the trace heat output. Options are 13 or 25 mm. 25 is difficult to form around bends and is considerably more expensive. It must be fitted tightly and have no gaps. Most important is that the insulation remains DRY, when it is wet you loose more heat than having none because of the increased surface area. You must use CLOSED cell foam insulation which is rather expensive at about £6 for a 2 metre length of 13 mm and it is not readily available from general plumbing suppliers. I use 32mm internal diameter for insulating external boiler condensate drain pipes. Hope you don't need a lot as you may find burying the pipe the regulatory 750mm -1350mm a cheaper option.