Yes a watertight seal is not as easy as it may seem. Even if you do get it watertight it may only last a year or a few months before you start to see condensation inside. Trust me take it for me I have done many headlight retrofits where I would bake headlights to open them up and make projectors and LED strips inside. The end result would look awesome and watertight but eventually water always finds a way in.
I too would like waiting for a company to actually remanufacture our side markers as a direct retrofit. Not sure why it is taking so long.