what is the best solution for raising of caramel wafer shelf life and be soft in all over its shelf life?
Are you considering the dutch syrup waffles?
The trick will be using emulsifiers, humectants and controlling the wateractivity.
Or you consume them as the dutch: The waffle itself will be quite dry, but we tend to heat them up above a cup of tea or coffee to make them soft again:)
Try keeping caramel filling water activity below 0,4. As this will make it thicker, you will need some ingredient aid, such as water trapping agents (glycerin, sorbitol..) and a good emulsifier, as Jos said above.
Controlling aw like this will mitigate water migration rate, keeping desired texture for a longer time, for both filling and wafer.