You can't expect an open fueling depot full of abandoned Tanker trucks to be claimed by one group or another. If they truly wanted to stake a claim to it, then guard it. 24/7. If this mission was so important, put your base there. Protect your most precious resource. Protect your weapons. At the end of society, yes the rules are gone because there's no one to enforce it but you. You're sticking to the fact that they staked an invisible claim to a material possession. It's the same concept of finding a new land and placing a flag on it. If you land 100 miles North of me, and I place a flag in the same land you claim for yourself how am I supposed to know? If you guard it, I know. If it's there for the taking, I'm taking it. You said so yourself: First come, first serve. Unless you are there to protect it, it's still first come first serve because you haven't made it clear it's yours.