How much water are you losing. Evaporation is expected and is just part of the game.
If you have a sump then you can look at auto top off systems that reduce the amount of effort you put in to it day to day.
Depending on how closly your ro is located to the tank you can do top off directly from the system with an auto shut off valve and a float in your sump (is that what you mean by wet dry?). If there isn't a sump the same thing can be done directly to your tank with an auto top system.
A lid will slow down evaporation but also effect how well 02 gets into your system and heat.