That sound like a much more simple option @dangerdarrell I now intend to give it a go, using the same method, when I fit my one.
I think that I'll fit a little stop collar, over the drill bit, to stop me drilling too deep. Does anybody have the dimension, for the depth of the panel, so that I can set the stop.
Stop collars, in picture above.
@UK_Paul the panel is probably only 1/8" to 3/16" thickness. You shouldn't have to worry about drilling through the tank, just drill slowly with a 1/8" bit until you feel your bit break through the plastic, then use a flashlight to confirm the metal tank strap is behind your pilot hole. Then drill out your hole to 8mm still taking care not to over penetrate. You never want to over penetrate. Please post up a pic when you get it on as I'll get a big charge out of seeing it on one out of less than 15 Slings on your side of the pond. Cheers!