The real question is whether any harm is going to even be noticed during the time you have the batteries. Do you RV two weeks and then do fifty weeks of floating, or do you go camping every month for a few days with floating in between trips?
There is some harm from floating deep cycle batteries as opposed to UPS batteries and I suppose floating them above the proper just right voltage will increase that. ( Mex pointed out antimony poisoning as being one effect that can happen. ) But should you worry about that? Batteries die anyway eventually.