I'm useless with them Catchelot, I've have a couple, run a number of times each for kingfish, and they look the business in the water, awesome vibration, but haven't caught a thing yet. I would suspect that has more to do with my lack of experience and poor technique than their fish catching abilities.
I tried one as a diver to get a marlin lure running below the surface one day just for kicks.
Interesting to learn more myself about their use.

Run them on lighter line, say 100lb flurocarbon, traces, but have a short say 2ft bite guard of single-strand wire, say 125lb. Have your flurocarbon leader tied to your mainline as a wind-on, assuming you are trolling with braid. Then there will be no need at all for a swivel.
Rapalas, or indeed pretty much any minnow lures, are deadly on kingies.



I prefer single strand wire as you can make good, small loops that are much less obvious and more streamlined than multi-strand wire loops, and you can tie them up without having to havecrimps on hand.
Have a small swivel on the end of the wire if you want, to tie the flurocarbon on to, or a small solid ring would do just as well. With the aim or reducing the number of bubble-making components in your trace, I personally would have a smallish b/bearing swivel, say a size 4, split ringed onto the lure itself, then the wire trace, to a small solid ring (stainless, not some anonymous muck metal like the surecatch ones you see around the place, NEVER use those with wire, it chews straight thru them!), tie that to your flurocarbon, and you hopefully should be OK.

Using a huge leader, like 400lb..... no, no way would I recommend that, it would be humungously obvious and I suspect it would interfere with the lures action.

Edit:.... just saw your post above Cachalot. Yes, bibbed minnows have taken billfish certainly, I know of two sailfish that have been taken on halcos in the sollies (not by me dammit), and yes, marlin on stickbaits and minnows certainly. The Bonito type "trembler" lures surely have, the bibbless minnows trolled often for wahoo and tuna, marlin smack them all the time.

I have seen couta take off my home made lures instantly

The single strand wire is a little less obvious than the multistrand, at least to my eye it is, and if you are hoping for some protection from teeth, such as coutas, then yes, I am afraid wire is your best choice.
Ideally I would say no, just use say 100lb flurocarbon trace, and accept that perhaps the odd lure may fall victim to teeth.
Check out the bargain bins in shops everywhere you go too, as often you will find cheap minnow lures in them. FCO had some good cheap 180mm bibbed minnows a while back, like $15ea or something I think, again, they do do the job adequately, and the ouch of losing them is markedly less :-) Certainly I would use lower price lures where you know or suspect coutas will bounce you, save the top shelf lures for safer waters, like in summer etc.
Oh, and when trolling around reefs for kings, do not be at all surprised if you pick up the odd good snapper too.
Also, maybe see if you can get some of the halco lures, the laser pros with the 8m bib are bloody lethal (no, not you Eric) on pretty much everything that swims, a hugely under-appreciated lure, at least here in NZ.

I have 4 of those x raps... cant catch a kingfish on them either... while in the same spread the cd18s have been slaying them.

Have caught Kingfish on the newer X Rap 30's, would be interested to try those Halco Laser Pros....will have to try them on some Northland Kingis!

I've tried the xrap's and the CDs... I cant say I have ever run them together at the same time....  so cant say for sure what is better...  but Ive caught way more kings on the xrap..    and they seem to run better at higher speed than the CDs in my experience.  

Thanks Vance, well that is surprising as those slithers had small hooks I think...just goes to show eh?

Just had a dig through my boxes and found one CD 18 with what looks like flimsy 3/0 trebles(so changed them for owner 3/0 Barbless) and two CD22's but these both had double hooks on.....look like a 4/0....so was thinking of changing them out for 4/0 owner trebles(barbless)......anyone tried like this and will it effect their action at all? thanks

The halco laser pro lures are a real old standard lure. My pref is for the ones with the super deep 8m+ bibs though...

...
oh, and as you can see, they are rigged on single strand wire too....