While it's far from certain, I believe it was the creepy camper. Why?
It sounds like these two women were 'bad-*advertiser censored* and knew how to defend themselves', so likely weren't put off too much by strange people. If someone creeped them out to the point that they pointed it out to others and said they would have to move camping spots, then their sixth-sense might have been bang on.
The other reason I am leaning toward the creeper theory is that the location where they were killed is isolated. how many people would they come across in that location? And yet they specifically mentioned a weirdo in that location.
And, finally, the manner in which they were killed implies rage with multiple shots in various parts of their bodies. Not a simple 'get off my land' kind of thing.
Regarding the half-nude aspect, I don't know what to think about that. If they were just bathing then I'd expect them to be fully naked. They could have been having sex and the killer was watching them and it offended him. Or, the killer could have made them strip to confirm they were both women and/or simply to show power over them by demeaning them.
Hopefully the FBI can move this case forward and get justice for Kylen & Crystal.