as long as it’s not too cool when you mix them, condensation is only an issue when you open cold concentrates and warm air meets cold air inside the bottle
You will only get condensation on the outside if you don’t open them while cold
I always let mine warm up before mixing and any that crystallIZe I just drop in a cup of warm water for a while
Have been using a fridge for years and never had an issue I personally don’t like the idea of leaving anything at room temperature for years but I only have 50 - 60 flavours so it’s easy for me