best way to seal sintra edges?

I never do any painting of sintra but some of my customers struggle with sealing the edges to get a nice finish. any ideas?

I do a lot of sintra stuff for my models and for my thin stuff I just use PVC cement to smooth out the edges. I think Joe uses a Gorilla pvc Glue. Russ

got one customer with 1" thick letters and they want to deal with the edges.

I use automotive Glaze putty like Bondo 907 But not the stuff that needs a hardener. Any good auto body supply place will have it or even auto parts