By protecting do you mean preventing them from fading? Keep them in a room that doesn't get sunlight, for example using blackout curtains. Or if there is sunlight don't let it be direct. Low humidity helps too. Basically keep the area climate controlled. If you want to limit dust put them in some sort of display case.
An old article of mine here discusses the lighting side of things. https://www.antique-bottles.net/show...ating-the-Past
But, in general, keep them away from light-- especially sunlight. I keep mine in a cabinet I close off when I don't want to look at them. Keep them away from high humidity. 50-70% is fine. Temperature isn't as much of a concern as some people think. Normal room temperature is sufficient.
Don't coat them in anything. No sprays. If for some reason you must coat one, Krylon puts out archival sprays for art work. It's sold at Hobby Lobby. Get matte, not semi-gloss. To reconstruct a label, use Elmer's Rubber Cement-- not glue, but rubber cement-- to reattach pieces. I recommend against clear plastic sleeves as labels need to breath and some plastics will leach chemicals into the paper, ruining the labels. I keep my best labels behind glass.
Yes these styro label sodas are now very hard to find in nice condition, as they were used for such a short time and we didn't save any, thinking they were just "new" and worthless. When I do see one...