I'd also plug it in if possible-to make sure they're as topped off as possible. The charge rate trickles down to very slow as the batteries approach full charge. Although you will get substantial charging in 6 hours of travel.
The time to charge is when you return from a trip. You don't want batteries sitting around in a semi discharged state-worst thing you can do. Get em fully charged when you return and disconnect to prevent parasitic losses. Many RVs operate detectors and other parasitic loads even when batteries are disconnected via disconnect switch.