My wife and I were out at Hobby Lobby looking for some of the Krylon clear coat, they were all out and she pointed out this other coating spray.
It's made by Tree House Studio, Clear Acrylic Matte Coating (for dull coating). I read the label and it's recommend for plastics. It cost around the same price as the krylon stuff at $5.50.
I tried it out on some light weathering with pastels and it didn't fade them out. It also dries fast too. Does 'claim' it wont yellow out, but I wouldn't know..
Just something to try out if you're interested in something else to coat your models with