It's definitely more common to have the EHU charger going to the LB, yes. As when you're staying somewhere for a few days the LB will be getting the most use, and unless you have solar and/or a hefty 200Ah lithium LB you'll need hookup to last more than 2-3 days.
Generally, you only need to worry about the SB if you've been staying somewhere for 4 or 5 days or longer, the only things that would drain it are the unlocking and locking of doors, electric sliding doors if you have them. You might need to top up the SB in this case, which can be done just with a 5a charger plugged in (via 240v hookup socket) into the cigarette lighter port on the dash on a T6. T6.1 12v sockets might be different, you basically need a permanent live 12v socket going to the starter battery.
FYI this is how mine is set up, I have a Victron 15a 240v charger connected to 240v hookup (all under the driver's seat), this feeds the LB. Then if I ever need to top up the SB I've got a separate 5a victron charger with a 12v socket adapter which I trickle the SB with from the 240v socket inside the van. At the moment I just have the std OEM split charge but this will be getting upgraded at some point.