GSDs are very attached to their families. It's in their makeup. They just want to be with you. It's one of the reasons they make great police dogs - they are dedicated to their handlers. This isn't necessarily "separation anxiety" as much as it is "why can't I be with you".
Questions to ask yourself:
How is the dog when you are home? Does she have problems when you leave her home alone? Is she OK if you are in the front yard talking to your neighbors?
If she doesn't have problems when you leave her alone at home, then it's not separation anxiety and medication is not the answer.
This may take you a bit of compromise in order to re-train her. Rather than tying her outside (in view of you) and spending 15+ minutes at another campsite, try putting her in the camper and spending just a few minutes with the neighbors. Then come back and praise her and spend time with her. As she becomes comfortable with your stepping away for a few minutes, you can build up the time - always giving her lots of attention when you return.
One thing to remember, is don't make a big deal when you put her in the camper and leave her. A simple "be good", close the door and walk away. You can also give her a cookie when you leave as a treat.
This is not an instant solution. Don't expect to spend one trip compromising your visits and then going back to your old routine. This will take time - likely an entire season. And you may have to "re-train" her at the beginning of future seasons.