Hi Dreamtime!

Here is some information you may find useful.

https://infrastructure.gov.au/vehicles/vehicle_regulation/bulletin/vsb1/vsb_01_b.aspx

Section 14 particularly.

Australian Design Rule 42/04, Section 9 - same information expressed in more "legal" way.

https://www.legislation.gov.au/Details/F2016C00153

 When I build non boat trailers I really go to some trouble to tack weld small square tube off cuts all along the trailer then push small round 

 rubber bushes along the cable and then into the tubes , a round peg really does fit in a square hole,,,,,,,,,,,,, go figure.

 Anyway for exsisting trailers I use rubber coated steel p clips found in bunnings or supercheap , repco etc, and use driven self tappers into the steel.

 You do have to support it on a measured distance found in the regs , dont quote me but thought its 300mm.

 I solder and heat shrink everything , and in putting 3 trailers over the pits ( private garages knowadays) havnt had a problem.

 Thanks fellas I had a look at the link you posted and its handy but limited as the only info I could find is actually exactly what I needed to know but not much else. The spacing regulations state that it must be supported every 600mm and located where it won't get chafed or come in contact with moving parts! Nothing on there about how to store excess cable either but I'll just see what they say tomorrow! Thanks again lads

 Scrap that there is actually a lot of info on that page once I looked at the whole lot!