It's all in what a couple want to do. Has nothing to do with what is right or wrong. Not sure the purpose of this post really. Why are YOU worried, or even have an opinion on what is "ok" for another couple to do?
I am retired military, and fortunately was only away for one short tour, other than a couple of short deployments here and there. I personally do not go RVing without my wife, because we both enjoy it, and we enjoy each others company. I have been known to go hunting by myself, and she makes trips to see her family time to time. She does an annual vacation with her sisters. I don't have a problem with it.
OP admittedly, I got sucked into your vortex, but I don't even really understand why you felt the need to even make this comment or observation.
Mike