For $600 you should be able to get a trunk monkey with a squeegee.
I found a perfect bottle back around 1998 or 99 and I mounted it in place on the fender to keep it safe. It sat protected for nearly 15 years until Paul looked it over in 2013. It had hardened to the point of being brittle and useless. What I don't know is why, some sort of chemical fumes in the garage or could it be the plastic gets brittle if it's left without any water? I don't know, but not knowing stops me from spending much coin for a NOS bottle.
I have read that plastic parts can be softened and made nice white again by simply putting them in a big pot of boiling water and boiled for a few minutes. The is also supposed to remove the yellow, rust color.
A short read.
My bottle "looks" ok but has a few holes on the bottom, so I have been pondering how to fix it. I'm going start with a big pot of boiling water on my BBQ and try the boil-it-to-soften-it. If I can reduce the brittleness it will make handling it easier. Then I'm going to experiment with liners.
Something that starts as a liquid and sets or dries into a transparent strong flexible film would be ideal. If clear or white can't be found, maybe painting the inside first would hide a darker liner. Maybe paint the inside with clearcoat, then inflate a nice thick skinned balloon inside. The balloon would bond to the clearcoat and make everything water tight.
For now my car is about 99% complete and my trunk stored bottle of Windex works just fine.