I haul with full tanks but for no other reason than to have plenty of water with me… but you are not going to get a lot of side to side sway from a half full tank in a RV…
Due to its low mounting and small size in a Partially filled RV fresh water tank, the shifting of the water would cause minimal sway force… enough of the water would quickly fill the one side of the tank and begin working against the sideways push of the remaining water acting like its own shock absorber in some respects… so there would be weight shifting but about the only shifting that would matter would be the initial water hitting against the flat side of the tank followed by the self dampening of the rest… the problem would be small and tank baffling would be almost no help in a small tank…
In a tank truck or tank trailer with loads on a higher centre of gravity and a long cylindrical tank the liquid in much higher volumes with longer distances of travel, baffles would make a big difference because even though the same amount of weight is being shifted it is being shifted shorter distances and again it begins to self dampen against the baffles…
I only have a 40 gal fresh water tank in the far rear of my trailer and if the shifting on the water can be felt or cause sway, that’s where it would show the most, I have never noticed it full or half full…