I generally use the key fob, because it locks all the doors at once, whether I'm locking myself in for the night or locking up before I leave during the day. I don't have to remember which
doors I unlocked during the day.
I've never had a fellow camper nearby ever complain about the marker lights flashing, any more than they would complain when a trailer owner uses the key fob to lock their truck and the lights flash. It might be different if the key fob caused the horn to honk or something— not that the wimpy OEM "neep, neep" horn would be disruptive to other campers, either…
But if you WANT to manually lock the doors of your Interstate to avoid flashing the marker lights, that's fine, too. It's your Interstate, you can do it the way you want.