What we've found out when using Corafoam (don't know how that compares to your stuff) is to use ALL 100% acryllic paint. Don't even have to put a finsh clear coat of any kind on it then. There are Corafoam sign carvers up here doing that and guaranteeing their work for 10 years. And these are the "pros" doing the big custom carved business signs.
Otherwise, you have to use either spar varnish or spar urathane with UV protection as a clear coat and recoat it every 2-3 years.
Last edited by honesttjohn; 06-30-2016 at 10:20 AM.