Yesterday I accidentally didn't answer your question today it's a bit more intentional.
Do I have direct experience of using a Zig Unit? No but I've read up a bit as I am interested in battery charging.
If you have read [You must be registered and logged in to see this link.]
it's not an easy read and all it authoritively concludes at this point is about 12S and 13pin wiring.
The general arguments for and against Zig Units are sumarised here: [You must be registered and logged in to see this link.] [You must be registered and logged in to see this link.]
Given that if you do any further readding on these sites they are motorhomes and 12v wiring is by earth return not isolated.
So the arguments against a Zig are generally it's expensive compared to a battery charger and a voltmeter also that it only charges to 13.8v so it doesn't fully charge the battery and because the maximum voltage is only 13.8v the rate of charge is very slow.
Having said that you have the Zig so cost isn't a consideration. Short term (even weeks) less than optimum battery charging isn't a major issue. They look nice and neat.
What Zig do you have? Answers will vary somewhat dependent on unit but here is an instruction leaflet for a Zig C.F.8 [You must be registered and logged in to see this link.]
So the Zig should when on mains charge the battery and provide a number of 12v supply circuits. Now the Zig unit will "sort of" (can't term it better than that) perform the function of a split charge relay when towing the Dandy. As may have been observed from reading the Zig leaflet PDF the instruction sheet is quite old, newer leaflets may offer differing advice. The suggestion to wire directly through pin 4 (pin9 on 13 pin plugs) without a split charge relay and only using a fuse. I personally wouldn't do this. With a newer car the Zig doesn't isolate the "Habitation" circuits while being towed. Even with an older vehicle I'd tend to want the advantages of quicker and more complete charging offered by a split charge relay. Though how I would wire one up in this case I'd need to think about.
If you didn't get round to reading [You must be registered and logged in to see this link.]
one final push of two points in there.
1) Fuses as close as possible to the battery terminals
. Personally I'd fuse both the +ve and -ve terminals this gives a second, second chance and batteries are unforgiving if shorted out.
2) As said by peridot. Check through the Dandy 12S wiring. If you are expecting it to be wired to any particular convention think again. The most obvious difference you may find is pin2 wired to the leisure battery (your car may well be wired that way) though as this Destiny has a Zig then again maybe not?
When returning home I'd remove the battery and charge with an intelligent charger.
Hope this is enough to get you started. Some of your options will be governed by how you want to camp be it permanent EHU or more wild camping.