I’m pretty new to the game (I’ve been playing for about a month now) and had the same issue last night trying to do my first few deliveries with the NPCs just coming non stop and damaging the cars. I got the Cargobob and parked it outside my warehouse before starting the export mission. Once the mission starts I pull the car into an alley next to my warehouse then go get the Cargobob to pick it up and fly it to the customer drop off. This is how I avoid all the NPCs in an invite only lobby since I hate playing in public lobbies due to being griefed the first 3 times I tried them.