I do this. It's a running joke in our truck because I get back a wave maybe 1 out of 20 times. I've even taking to rolling my window down and waving idiotically (though, we've been afraid that maybe I'm alarming people into thinking their is something wrong!).
The real problem is- most of the time, the sun glare is such that you can't be seen until you and the other RVer are right on top of and passing each other.
But, I'll continue to wave- even if for no other reason than to have a running count of who does/doesn't wave.