National code (from memory) sez only one central neutral to ground tie, at the first distribution box after meter. But if you don't have a separate ground wire from that box to your camper location service equipment I'd for sure drive a ground rod tie to the service box ground bar and camper outlet. I'm a bit undecided about whether to keep those grounds separated from the neutral at a remote box with no ground wire tied back to that central ground point. Personally I think I would jumper the ground bar to the neutral bar in that remote service equipment. Always keep ground wires on a separate bar from the neutral bar. VERY important to have great grounds for campers. Easy to end up with a hot camper chassis and get a nasty shock or electrocuted stepping out the door! Triplex (twisted service wiring) both above and underground acts as a transformer, Neutral wires can get quite "hot" having a surprisingly high voltage compared to ground.
There was a guy on another forum, was a traveling campground electrical safety expert. Long runs of wiring in a harsh environment with constantly increasing electrical loads were (are) hotbeds of ground problems. He carried a tester that you could plug into the camper supply outlet that showed problems. He said bad grounds and "hot" neutrals were rampant in campgrounds and I completely believe him. I've never been an electrician but sold electrical supplies and did a lot of work with campgrounds.AND farmers through the "stray voltage" issues and lawsuit era, we learned alot about cause and effect of neutrals, grounds, establishing ground planes. Barefoot cows standing on wet ground with equipment attached to their teats are understandably sensitive about stray voltage!