I deleted my first reply as it wasn't really good advice as I'm not fully aware of your camping style, so suffice to say if you are free camping a lot, have solar to power up your batteries whilst travelling then 12v tug to van for charging isn't really a biggy the solar should take care of it all otherwise you would be in trouble in camp, I've already mentioned my view of running fridge on 12v, if you are predominately camping with 240v supply then charging as you go down the road isn't really needed either as they should be kept charged when plugged into 240..................though if you don't have solar and aim to camp for a few days free camping without using a genny then the 12v charg from car is required so when you arrive everything is juiced up and can be recharged when you leave, trying to charge at camp by runnning the vehicle is not a great idea, idling a vehicle for long periods doesn't do them any good, burns heaps of fuel for not a great deal of charge unless you want run it for hours.....a standard alternator to provide high charge needs to run higher than idle......hence a genny is a better idea.
Of course others may tend to disagree, there are numerous views on the subject.... No use fitting something at great expense if its hardly used.
My rig doesn't get 12v from tug as solar powers it all, rarely camp with 240v supply and if need 240 when free camping we fire up the genny, fridge on gas and all appliances other than the washing machine run on 12v.................free camp for a week at a time and drive for maybe 4-5 hrs once a week when we move.....