I agree. When I want to maintain mosses outside an aquascape I put them in a flattish plastic container with a clear lid. I put a layer of Fluval substrate or ADA Aquasoil on the bottom, them saturate it with water. Then I just lay the moss on top of the wet soil and close it up. I keep it in a bright room, with INDIRECT sun light. It is never in direct sunlight. I have found that mosses do very well this way, and reproduce readily.
I have not had good luck growing even "easy" mosses on the windowsill. I think they get too warm in the sun light.