Direct cable run via andersons to fridge as stated above, regarding smart alternators it really depends on the vehicle, not all are the same and even model year can be different set ups, some supposedly smart ones aren't really, so best to get the correct information on yours, usually not from a dealer ....... Ford Rangers of a few years ago direct POS to the actual POS terminal on battery and NEG to chassis/battery ground point not on battery but later models need something different...... then Jeep Grand Cherokees have a jump start points under bonnet, AGM under the seat, no smart alternator so hook up is simple, straight onto jumper points so you know the wiring is certainly HD.
I prefer the Fridge Switch located in van, stopping in traffic really isn't an issue, maybe if you were stuck for an hour or so and in that case you wouldn't be idling the engine that long anyway, besides I have forgotten to turn my fridge on to 12v and went for 5 hours in 35 deg back of Winton and it had an increase of 2 deg, so a fridge switch set up in the van isn't going to make any more difference than opening the door ................ In all my travels accidents have held me up for hours but then we sat in van with fridge on gas having a cuppa.............. Ideal fridge temp is fridge 4 deg, freezer -12 ....