I would run the ignition feed.
I didn't initially and the engine shut down detection is a pain in the arse to get right, due to the van's alternator only charging the starter battery to 70% and then only topping up battery on deceleration.
The starter voltage can be seen as low as 12.1v for reasonable durations when the BMS has decided that no more voltage is necessary and this plays havoc with trying to configure the shutdown detection so that the dc-dc charger isn't cycling power more regularly than it should.