You could investigate the use of "Eurethane" windcreen adhesive. Its very strong and sets to a very rubber like consistency. Set time used to be 3 hours with a 24 hour fully cured time.
Benefits are it can be piped into a mould with a caulking gun as it comes in cartridges, it does not leave a black rubber ring around your eye once you wash it, and takes on the relief of the mold, so shiny or textured depending on mold.
It used to be expensive but it is very very common now, just beg borrow buy a cartridge from someone that fits/replaces auto windscreens for a trial run, they might even have a part cartridge they are throwing out.
Easy to trim with a stanley blade and a bit of water.
Not sure about any downside.......oh yes, it is really messy straight out of the cartridge so some dexterity is required to avoid getting it over yourself, clothes, door handles, benchtops and ultimately the Mrs......
Clean up excess easily with kerosene on a cloth.