As I don't have (or want) a caravan, no. But I'm so close to being able to drive the bus I don't care. So, as I see it, I connect 12V to the bus battery. 0 to earth and 6 to the leisure battery all will be well. I presume it won't need a massive wire to the Leisure battery?
You'll want around a 16amp cable for that... but just mind the voltage on the leisure battery... if it gets low it could cause the wiring to get warm while it's recharging!!
Wire size depends on the fuse you are fitting i would use 30amp wire and 30amp fuses http://www.vehicle-wiring-products.eu/VWP-onlinestore/cable/standardcable.php
I very much doubt that you could fit 30amp cable to that unit dude.. are you familiar with the green terminal blocks?
I see your point i see the relay is rated at 30amp so it should take the cable and as you said any smaller and it could get a bit hot when the battery is low.
I don't personally like them... I prefer to put something in that is rated to 100amps... overkill, but more likely to last!! Plus a really flat battery can pull 20-40amps
I have two linked vehicle batteries on board in the rngine bay so the leisure battery under the seat only powers the Propex and in emergencies (Mrs TBR's hair needs drying) the inverter. It's a huge 110a thing that I've never been able to flatten and it has its own conditioning charger that kicks in when on hook up. I think it'll be fine and it does have an inline fuse in case things go wrong.
